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 $95.44   3.339%   $98.6267   $98.63   $98.65   $98.60  
  Purchase #2 $38.83   6.128%   $41.2095   $41.21   $41.20   $41.20  
  Purchase #3 $15.88   4.387%   $16.5767   $16.58   $16.60   $16.60  
  Purchase #4 $185.96   8.275%   $201.3482   $201.35   $201.35   $201.30  
  Purchase #5 $96.81   5.613%   $102.2439   $102.24   $102.25   $102.20  
  Purchase #6 $34.97   5.653%   $36.9469   $36.95   $36.95   $36.90  
  Purchase #7 $227.54   6.484%   $242.2937   $242.29   $242.30   $242.30  
  7 purchase totals = $695.43       $739.2456   $739.25   $739.30   $739.10