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 $195.70   3.212%   $201.9859   $201.99   $202.00   $202.00  
  Purchase #2 $21.66   7.417%   $23.2665   $23.27   $23.25   $23.30  
  Purchase #3 $48.45   13.785%   $55.1288   $55.13   $55.15   $55.10  
  Purchase #4 $183.54   11.831%   $205.2546   $205.25   $205.25   $205.30  
  Purchase #5 $158.98   9.596%   $174.2357   $174.24   $174.25   $174.20  
  Purchase #6 $24.54   5.224%   $25.822   $25.82   $25.80   $25.80  
  Purchase #7 $53.80   4.722%   $56.3404   $56.34   $56.35   $56.30  
  7 purchase totals = $686.67       $742.0339   $742.04   $742.05   $742.00