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 $67.41   11.281%   $75.0145   $75.01   $75.00   $75.00  
  Purchase #2 $80.76   13.250%   $91.4607   $91.46   $91.45   $91.50  
  Purchase #3 $75.64   8.587%   $82.1352   $82.14   $82.15   $82.10  
  Purchase #4 $111.55   13.536%   $126.6494   $126.65   $126.65   $126.60  
  Purchase #5 $168.28   11.758%   $188.0664   $188.07   $188.05   $188.10  
  Purchase #6 $196.47   4.840%   $205.9791   $205.98   $206.00   $206.00  
  Purchase #7 $122.96   7.475%   $132.1513   $132.15   $132.15   $132.20  
  7 purchase totals = $823.07       $901.4566   $901.46   $901.45   $901.50