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 $219.70   11.861%   $245.7586   $245.76   $245.75   $245.80  
  Purchase #2 $157.60   8.283%   $170.654   $170.65   $170.65   $170.70  
  Purchase #3 $92.53   10.769%   $102.4946   $102.49   $102.50   $102.50  
  Purchase #4 $241.78   5.608%   $255.339   $255.34   $255.35   $255.30  
  Purchase #5 $144.42   11.427%   $160.9229   $160.92   $160.90   $160.90  
  Purchase #6 $226.52   12.339%   $254.4703   $254.47   $254.45   $254.50  
  Purchase #7 $151.59   4.575%   $158.5252   $158.53   $158.55   $158.50  
  7 purchase totals = $1,234.14       $1,348.1646   $1,348.16   $1,348.15   $1,348.20