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 $169.77   11.290%   $188.937   $188.94   $188.95   $188.90  
  Purchase #2 $22.49   7.440%   $24.1633   $24.16   $24.15   $24.20  
  Purchase #3 $31.48   4.812%   $32.9948   $32.99   $33.00   $33.00  
  Purchase #4 $41.50   10.285%   $45.7683   $45.77   $45.75   $45.80  
  Purchase #5 $228.77   13.652%   $260.0017   $260.00   $260.00   $260.00  
  Purchase #6 $155.27   3.815%   $161.1936   $161.19   $161.20   $161.20  
  Purchase #7 $224.48   8.469%   $243.4912   $243.49   $243.50   $243.50  
  7 purchase totals = $873.76       $956.5499   $956.54   $956.55   $956.60