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 $58.47   8.627%   $63.5142   $63.51   $63.50   $63.50  
  Purchase #2 $83.69   7.590%   $90.0421   $90.04   $90.05   $90.00  
  Purchase #3 $241.88   7.193%   $259.2784   $259.28   $259.30   $259.30  
  Purchase #4 $178.93   8.251%   $193.6935   $193.69   $193.70   $193.70  
  Purchase #5 $46.95   5.103%   $49.3459   $49.35   $49.35   $49.30  
  Purchase #6 $150.94   12.284%   $169.4815   $169.48   $169.50   $169.50  
  Purchase #7 $20.48   8.754%   $22.2728   $22.27   $22.25   $22.30  
  7 purchase totals = $781.34       $847.6284   $847.62   $847.65   $847.60