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 $176.76   10.476%   $195.2774   $195.28   $195.30   $195.30  
  Purchase #2 $77.44   12.238%   $86.9171   $86.92   $86.90   $86.90  
  Purchase #3 $112.81   6.226%   $119.8336   $119.83   $119.85   $119.80  
  Purchase #4 $152.27   4.328%   $158.8602   $158.86   $158.85   $158.90  
  Purchase #5 $39.47   3.243%   $40.75   $40.75   $40.75   $40.80  
  Purchase #6 $83.82   8.831%   $91.2221   $91.22   $91.20   $91.20  
  Purchase #7 $178.45   13.121%   $201.8644   $201.86   $201.85   $201.90  
  7 purchase totals = $821.02       $894.7248   $894.72   $894.70   $894.80