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 $188.77   11.131%   $209.782   $209.78   $209.80   $209.80  
  Purchase #2 $57.38   9.479%   $62.8191   $62.82   $62.80   $62.80  
  Purchase #3 $236.49   8.701%   $257.067   $257.07   $257.05   $257.10  
  Purchase #4 $201.87   5.522%   $213.0173   $213.02   $213.00   $213.00  
  Purchase #5 $56.86   10.735%   $62.9639   $62.96   $62.95   $63.00  
  Purchase #6 $85.92   10.864%   $95.2543   $95.25   $95.25   $95.30  
  Purchase #7 $146.87   5.543%   $155.011   $155.01   $155.00   $155.00  
  7 purchase totals = $974.16       $1,055.9146   $1,055.91   $1,055.85   $1,056.00