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 $84.83   11.731%   $94.7814   $94.78   $94.80   $94.80  
  Purchase #2 $55.72   11.409%   $62.0771   $62.08   $62.10   $62.10  
  Purchase #3 $188.46   11.770%   $210.6417   $210.64   $210.65   $210.60  
  Purchase #4 $23.88   13.860%   $27.1898   $27.19   $27.20   $27.20  
  Purchase #5 $121.51   9.405%   $132.938   $132.94   $132.95   $132.90  
  Purchase #6 $176.27   3.528%   $182.4888   $182.49   $182.50   $182.50  
  Purchase #7 $217.81   10.574%   $240.8412   $240.84   $240.85   $240.80  
  7 purchase totals = $868.48       $950.9580   $950.96   $951.05   $950.90