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 $56.83   10.773%   $62.9523   $62.95   $62.95   $63.00  
  Purchase #2 $115.56   5.258%   $121.6361   $121.64   $121.65   $121.60  
  Purchase #3 $16.83   6.543%   $17.9312   $17.93   $17.95   $17.90  
  Purchase #4 $155.97   5.601%   $164.7059   $164.71   $164.70   $164.70  
  Purchase #5 $234.33   7.251%   $251.3213   $251.32   $251.30   $251.30  
  Purchase #6 $160.87   5.488%   $169.6985   $169.70   $169.70   $169.70  
  Purchase #7 $159.90   11.206%   $177.8184   $177.82   $177.80   $177.80  
  7 purchase totals = $900.29       $966.0637   $966.07   $966.05   $966.00