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 $83.25   12.238%   $93.4381   $93.44   $93.45   $93.40  
  Purchase #2 $204.79   10.831%   $226.9708   $226.97   $226.95   $227.00  
  Purchase #3 $65.39   4.266%   $68.1795   $68.18   $68.20   $68.20  
  Purchase #4 $46.89   3.644%   $48.5987   $48.60   $48.60   $48.60  
  Purchase #5 $129.47   11.147%   $143.902   $143.90   $143.90   $143.90  
  Purchase #6 $118.75   7.703%   $127.8973   $127.90   $127.90   $127.90  
  Purchase #7 $178.84   13.797%   $203.5146   $203.51   $203.50   $203.50  
  7 purchase totals = $827.38       $912.5010   $912.50   $912.50   $912.50