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 $26.62   4.821%   $27.9034   $27.90   $27.90   $27.90  
  Purchase #2 $142.64   12.690%   $160.741   $160.74   $160.75   $160.70  
  Purchase #3 $110.26   10.126%   $121.4249   $121.42   $121.40   $121.40  
  Purchase #4 $30.78   9.547%   $33.7186   $33.72   $33.70   $33.70  
  Purchase #5 $133.71   13.480%   $151.7341   $151.73   $151.75   $151.70  
  Purchase #6 $118.65   10.293%   $130.8626   $130.86   $130.85   $130.90  
  Purchase #7 $170.53   7.857%   $183.9285   $183.93   $183.95   $183.90  
  7 purchase totals = $733.19       $810.3131   $810.30   $810.30   $810.20