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 $32.91   10.193%   $36.2645   $36.26   $36.25   $36.30  
  Purchase #2 $221.26   13.317%   $250.7252   $250.73   $250.75   $250.70  
  Purchase #3 $204.58   3.806%   $212.3663   $212.37   $212.35   $212.40  
  Purchase #4 $250.34   8.246%   $270.983   $270.98   $271.00   $271.00  
  Purchase #5 $170.49   7.698%   $183.6143   $183.61   $183.60   $183.60  
  Purchase #6 $37.43   8.345%   $40.5535   $40.55   $40.55   $40.60  
  Purchase #7 $203.96   10.272%   $224.9108   $224.91   $224.90   $224.90  
  7 purchase totals = $1,120.97       $1,219.4176   $1,219.41   $1,219.40   $1,219.50