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 $49.58   6.179%   $52.6435   $52.64   $52.65   $52.60  
  Purchase #2 $213.94   3.829%   $222.1318   $222.13   $222.15   $222.10  
  Purchase #3 $159.35   8.247%   $172.4916   $172.49   $172.50   $172.50  
  Purchase #4 $84.54   4.391%   $88.2522   $88.25   $88.25   $88.30  
  Purchase #5 $177.77   13.466%   $201.7085   $201.71   $201.70   $201.70  
  Purchase #6 $232.71   9.815%   $255.5505   $255.55   $255.55   $255.60  
  Purchase #7 $56.79   3.824%   $58.9616   $58.96   $58.95   $59.00  
  7 purchase totals = $974.68       $1,051.7397   $1,051.73   $1,051.75   $1,051.80