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 $119.28   5.142%   $125.4134   $125.41   $125.40   $125.40  
  Purchase #2 $158.35   9.144%   $172.8295   $172.83   $172.85   $172.80  
  Purchase #3 $238.53   7.313%   $255.9737   $255.97   $255.95   $256.00  
  Purchase #4 $39.62   12.501%   $44.5729   $44.57   $44.55   $44.60  
  Purchase #5 $101.87   8.865%   $110.9008   $110.90   $110.90   $110.90  
  Purchase #6 $145.83   6.109%   $154.7388   $154.74   $154.75   $154.70  
  Purchase #7 $101.43   7.201%   $108.734   $108.73   $108.75   $108.70  
  7 purchase totals = $904.91       $973.1631   $973.15   $973.15   $973.10