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 $24.35   3.655%   $25.24   $25.24   $25.25   $25.20  
  Purchase #2 $194.37   5.293%   $204.658   $204.66   $204.65   $204.70  
  Purchase #3 $153.47   5.630%   $162.1104   $162.11   $162.10   $162.10  
  Purchase #4 $175.30   3.115%   $180.7606   $180.76   $180.75   $180.80  
  Purchase #5 $119.51   9.482%   $130.8419   $130.84   $130.85   $130.80  
  Purchase #6 $115.88   8.705%   $125.9674   $125.97   $125.95   $126.00  
  Purchase #7 $35.65   6.477%   $37.9591   $37.96   $37.95   $38.00  
  7 purchase totals = $818.53       $867.5374   $867.54   $867.50   $867.60