Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $125.86   13.355%   $142.6686   $142.67   $142.65   $142.70  
  Purchase #2 $147.59   10.405%   $162.9467   $162.95   $162.95   $162.90  
  Purchase #3 $245.91   8.458%   $266.7091   $266.71   $266.70   $266.70  
  Purchase #4 $210.44   12.355%   $236.4399   $236.44   $236.45   $236.40  
  Purchase #5 $95.56   12.119%   $107.1409   $107.14   $107.15   $107.10  
  Purchase #6 $232.32   5.353%   $244.7561   $244.76   $244.75   $244.80  
  Purchase #7 $147.75   12.427%   $166.1109   $166.11   $166.10   $166.10  
  7 purchase totals = $1,205.43       $1,326.7722   $1,326.78   $1,326.75   $1,326.70