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 $73.52   11.154%   $81.7204   $81.72   $81.70   $81.70  
  Purchase #2 $209.54   6.661%   $223.4975   $223.50   $223.50   $223.50  
  Purchase #3 $61.96   9.808%   $68.037   $68.04   $68.05   $68.00  
  Purchase #4 $167.72   8.717%   $182.3402   $182.34   $182.35   $182.30  
  Purchase #5 $63.30   4.838%   $66.3625   $66.36   $66.35   $66.40  
  Purchase #6 $236.42   10.380%   $260.9604   $260.96   $260.95   $261.00  
  Purchase #7 $186.50   7.546%   $200.5733   $200.57   $200.55   $200.60  
  7 purchase totals = $998.96       $1,083.4913   $1,083.49   $1,083.45   $1,083.50