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   8.790%   $263.1956   $263.20   $263.20   $263.20  
  Purchase #2 $119.79   13.551%   $136.0227   $136.02   $136.00   $136.00  
  Purchase #3 $215.50   5.211%   $226.7297   $226.73   $226.75   $226.70  
  Purchase #4 $149.43   10.307%   $164.8318   $164.83   $164.85   $164.80  
  Purchase #5 $14.50   5.813%   $15.3429   $15.34   $15.35   $15.30  
  Purchase #6 $60.56   8.649%   $65.7978   $65.80   $65.80   $65.80  
  Purchase #7 $33.67   4.496%   $35.1838   $35.18   $35.20   $35.20  
  7 purchase totals = $835.38       $907.1043   $907.10   $907.15   $907.00