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 $241.93   7.555%   $260.2078   $260.21   $260.20   $260.20  
  Purchase #2 $70.88   5.443%   $74.738   $74.74   $74.75   $74.70  
  Purchase #3 $33.59   3.429%   $34.7418   $34.74   $34.75   $34.70  
  Purchase #4 $194.35   9.577%   $212.9629   $212.96   $212.95   $213.00  
  Purchase #5 $117.43   6.853%   $125.4775   $125.48   $125.50   $125.50  
  Purchase #6 $127.56   13.609%   $144.9196   $144.92   $144.90   $144.90  
  Purchase #7 $248.93   5.709%   $263.1414   $263.14   $263.15   $263.10  
  7 purchase totals = $1,034.67       $1,116.1890   $1,116.19   $1,116.20   $1,116.10