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 $250.40   7.364%   $268.8395   $268.84   $268.85   $268.80  
  Purchase #2 $217.70   12.353%   $244.5925   $244.59   $244.60   $244.60  
  Purchase #3 $92.95   4.193%   $96.8474   $96.85   $96.85   $96.80  
  Purchase #4 $127.43   11.473%   $142.05   $142.05   $142.05   $142.10  
  Purchase #5 $206.68   4.541%   $216.0653   $216.07   $216.05   $216.10  
  Purchase #6 $140.54   10.801%   $155.7197   $155.72   $155.70   $155.70  
  Purchase #7 $232.78   3.315%   $240.4967   $240.50   $240.50   $240.50  
  7 purchase totals = $1,268.48       $1,364.6111   $1,364.62   $1,364.60   $1,364.60