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 $240.66   4.797%   $252.2045   $252.20   $252.20   $252.20  
  Purchase #2 $194.44   8.377%   $210.7282   $210.73   $210.75   $210.70  
  Purchase #3 $111.33   6.869%   $118.9773   $118.98   $119.00   $119.00  
  Purchase #4 $158.35   11.831%   $177.0844   $177.08   $177.10   $177.10  
  Purchase #5 $71.88   3.296%   $74.2492   $74.25   $74.25   $74.20  
  Purchase #6 $83.91   10.239%   $92.5015   $92.50   $92.50   $92.50  
  Purchase #7 $218.92   11.556%   $244.2184   $244.22   $244.20   $244.20  
  7 purchase totals = $1,079.49       $1,169.9635   $1,169.96   $1,170.00   $1,169.90