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 $78.88   7.277%   $84.6201   $84.62   $84.60   $84.60  
  Purchase #2 $191.57   7.813%   $206.5374   $206.54   $206.55   $206.50  
  Purchase #3 $118.67   5.573%   $125.2835   $125.28   $125.30   $125.30  
  Purchase #4 $21.85   10.732%   $24.1949   $24.19   $24.20   $24.20  
  Purchase #5 $164.97   4.304%   $172.0703   $172.07   $172.05   $172.10  
  Purchase #6 $154.94   10.850%   $171.751   $171.75   $171.75   $171.80  
  Purchase #7 $123.47   5.459%   $130.2102   $130.21   $130.20   $130.20  
  7 purchase totals = $854.35       $914.6674   $914.66   $914.65   $914.70