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 $84.50   8.571%   $91.7425   $91.74   $91.75   $91.70  
  Purchase #2 $138.38   6.681%   $147.6252   $147.63   $147.65   $147.60  
  Purchase #3 $138.78   13.261%   $157.1836   $157.18   $157.20   $157.20  
  Purchase #4 $161.33   12.761%   $181.9173   $181.92   $181.90   $181.90  
  Purchase #5 $210.51   7.537%   $226.3761   $226.38   $226.40   $226.40  
  Purchase #6 $112.45   8.442%   $121.943   $121.94   $121.95   $121.90  
  Purchase #7 $6.42   5.176%   $6.7523   $6.75   $6.75   $6.80  
  7 purchase totals = $852.37       $933.5400   $933.54   $933.60   $933.50