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 $125.91   13.446%   $142.8399   $142.84   $142.85   $142.80  
  Purchase #2 $235.86   6.551%   $251.3112   $251.31   $251.30   $251.30  
  Purchase #3 $232.48   11.477%   $259.1617   $259.16   $259.15   $259.20  
  Purchase #4 $234.55   4.793%   $245.792   $245.79   $245.80   $245.80  
  Purchase #5 $162.46   3.667%   $168.4174   $168.42   $168.40   $168.40  
  Purchase #6 $224.79   9.426%   $245.9787   $245.98   $246.00   $246.00  
  Purchase #7 $159.83   12.577%   $179.9318   $179.93   $179.95   $179.90  
  7 purchase totals = $1,375.88       $1,493.4327   $1,493.43   $1,493.45   $1,493.40