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 $175.59   10.838%   $194.6204   $194.62   $194.60   $194.60  
  Purchase #2 $33.72   6.274%   $35.8356   $35.84   $35.85   $35.80  
  Purchase #3 $210.27   8.430%   $227.9958   $228.00   $228.00   $228.00  
  Purchase #4 $224.51   8.780%   $244.222   $244.22   $244.20   $244.20  
  Purchase #5 $90.71   11.491%   $101.1335   $101.13   $101.15   $101.10  
  Purchase #6 $168.40   8.786%   $183.1956   $183.20   $183.20   $183.20  
  Purchase #7 $245.60   13.571%   $278.9304   $278.93   $278.95   $278.90  
  7 purchase totals = $1,148.80       $1,265.9333   $1,265.94   $1,265.95   $1,265.80