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 $83.41   10.303%   $92.0037   $92.00   $92.00   $92.00  
  Purchase #2 $155.78   11.812%   $174.1807   $174.18   $174.20   $174.20  
  Purchase #3 $136.69   11.229%   $152.0389   $152.04   $152.05   $152.00  
  Purchase #4 $57.53   6.242%   $61.121   $61.12   $61.10   $61.10  
  Purchase #5 $172.28   13.707%   $195.8944   $195.89   $195.90   $195.90  
  Purchase #6 $179.63   12.119%   $201.3994   $201.40   $201.40   $201.40  
  Purchase #7 $7.64   9.396%   $8.3579   $8.36   $8.35   $8.40  
  7 purchase totals = $792.96       $884.9960   $884.99   $885.00   $885.00