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 $207.94   6.628%   $221.7223   $221.72   $221.70   $221.70  
  Purchase #2 $13.84   3.738%   $14.3573   $14.36   $14.35   $14.40  
  Purchase #3 $111.63   7.244%   $119.7165   $119.72   $119.70   $119.70  
  Purchase #4 $110.72   5.116%   $116.3844   $116.38   $116.40   $116.40  
  Purchase #5 $29.67   4.255%   $30.9325   $30.93   $30.95   $30.90  
  Purchase #6 $22.97   7.206%   $24.6252   $24.63   $24.65   $24.60  
  Purchase #7 $209.96   11.782%   $234.6975   $234.70   $234.70   $234.70  
  7 purchase totals = $706.73       $762.4357   $762.44   $762.45   $762.40