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 $206.49   10.432%   $228.031   $228.03   $228.05   $228.00  
  Purchase #2 $35.45   4.239%   $36.9527   $36.95   $36.95   $37.00  
  Purchase #3 $49.84   4.139%   $51.9029   $51.90   $51.90   $51.90  
  Purchase #4 $201.87   12.409%   $226.92   $226.92   $226.90   $226.90  
  Purchase #5 $45.39   9.682%   $49.7847   $49.78   $49.80   $49.80  
  Purchase #6 $10.86   3.120%   $11.1988   $11.20   $11.20   $11.20  
  Purchase #7 $219.42   4.425%   $229.1293   $229.13   $229.15   $229.10  
  7 purchase totals = $769.32       $833.9194   $833.91   $833.95   $833.90