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 $84.44   13.160%   $95.5523   $95.55   $95.55   $95.60  
  Purchase #2 $125.25   7.579%   $134.7427   $134.74   $134.75   $134.70  
  Purchase #3 $95.56   7.249%   $102.4871   $102.49   $102.50   $102.50  
  Purchase #4 $183.35   7.781%   $197.6165   $197.62   $197.60   $197.60  
  Purchase #5 $60.96   10.625%   $67.437   $67.44   $67.45   $67.40  
  Purchase #6 $243.63   3.832%   $252.9659   $252.97   $252.95   $253.00  
  Purchase #7 $123.28   9.449%   $134.9287   $134.93   $134.95   $134.90  
  7 purchase totals = $916.47       $985.7302   $985.74   $985.75   $985.70