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 $187.92   3.252%   $194.0312   $194.03   $194.05   $194.00  
  Purchase #2 $189.91   11.766%   $212.2548   $212.25   $212.25   $212.30  
  Purchase #3 $208.43   7.818%   $224.7251   $224.73   $224.75   $224.70  
  Purchase #4 $98.38   13.442%   $111.6042   $111.60   $111.60   $111.60  
  Purchase #5 $169.76   8.602%   $184.3628   $184.36   $184.35   $184.40  
  Purchase #6 $223.94   7.795%   $241.3961   $241.40   $241.40   $241.40  
  Purchase #7 $81.60   6.132%   $86.6037   $86.60   $86.60   $86.60  
  7 purchase totals = $1,159.94       $1,254.9779   $1,254.97   $1,255.00   $1,255.00