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 $201.97   11.150%   $224.4897   $224.49   $224.50   $224.50  
  Purchase #2 $172.35   3.679%   $178.6908   $178.69   $178.70   $178.70  
  Purchase #3 $32.97   11.459%   $36.748   $36.75   $36.75   $36.70  
  Purchase #4 $194.50   7.743%   $209.5601   $209.56   $209.55   $209.60  
  Purchase #5 $69.35   9.179%   $75.7156   $75.72   $75.70   $75.70  
  Purchase #6 $146.34   9.798%   $160.6784   $160.68   $160.70   $160.70  
  Purchase #7 $17.41   5.181%   $18.312   $18.31   $18.30   $18.30  
  7 purchase totals = $834.89       $904.1946   $904.20   $904.20   $904.20