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 $213.76   7.254%   $229.2662   $229.27   $229.25   $229.30  
  Purchase #2 $22.98   6.160%   $24.3956   $24.40   $24.40   $24.40  
  Purchase #3 $246.43   4.433%   $257.3542   $257.35   $257.35   $257.40  
  Purchase #4 $219.59   11.128%   $244.026   $244.03   $244.05   $244.00  
  Purchase #5 $158.69   7.601%   $170.752   $170.75   $170.75   $170.80  
  Purchase #6 $207.37   11.350%   $230.9065   $230.91   $230.90   $230.90  
  Purchase #7 $32.66   7.583%   $35.1366   $35.14   $35.15   $35.10  
  7 purchase totals = $1,101.48       $1,191.8371   $1,191.85   $1,191.85   $1,191.90