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 $236.57   10.823%   $262.174   $262.17   $262.15   $262.20  
  Purchase #2 $163.54   11.475%   $182.3062   $182.31   $182.30   $182.30  
  Purchase #3 $164.64   4.639%   $172.2776   $172.28   $172.30   $172.30  
  Purchase #4 $144.63   5.289%   $152.2795   $152.28   $152.30   $152.30  
  Purchase #5 $132.99   6.205%   $141.242   $141.24   $141.25   $141.20  
  Purchase #6 $131.98   13.363%   $149.6165   $149.62   $149.60   $149.60  
  Purchase #7 $200.66   11.409%   $223.5533   $223.55   $223.55   $223.60  
  7 purchase totals = $1,175.01       $1,283.4491   $1,283.45   $1,283.45   $1,283.50