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 $202.43   4.209%   $210.9503   $210.95   $210.95   $211.00  
  Purchase #2 $64.79   3.357%   $66.965   $66.97   $66.95   $67.00  
  Purchase #3 $103.56   6.305%   $110.0895   $110.09   $110.10   $110.10  
  Purchase #4 $167.98   5.306%   $176.893   $176.89   $176.90   $176.90  
  Purchase #5 $146.84   3.637%   $152.1806   $152.18   $152.20   $152.20  
  Purchase #6 $118.37   11.701%   $132.2205   $132.22   $132.20   $132.20  
  Purchase #7 $39.73   4.475%   $41.5079   $41.51   $41.50   $41.50  
  7 purchase totals = $843.70       $890.8068   $890.81   $890.80   $890.90