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 $56.87   9.543%   $62.2971   $62.30   $62.30   $62.30  
  Purchase #2 $6.43   5.221%   $6.7657   $6.77   $6.75   $6.80  
  Purchase #3 $118.39   11.618%   $132.1446   $132.14   $132.15   $132.10  
  Purchase #4 $86.40   8.792%   $93.9963   $94.00   $94.00   $94.00  
  Purchase #5 $203.51   4.839%   $213.3578   $213.36   $213.35   $213.40  
  Purchase #6 $185.43   11.665%   $207.0604   $207.06   $207.05   $207.10  
  Purchase #7 $244.38   5.822%   $258.6078   $258.61   $258.60   $258.60  
  7 purchase totals = $901.41       $974.2297   $974.24   $974.20   $974.30