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 $10.38   6.244%   $11.0281   $11.03   $11.05   $11.00  
  Purchase #2 $36.51   9.527%   $39.9883   $39.99   $40.00   $40.00  
  Purchase #3 $34.60   7.435%   $37.1725   $37.17   $37.15   $37.20  
  Purchase #4 $156.49   11.397%   $174.3252   $174.33   $174.35   $174.30  
  Purchase #5 $157.94   4.668%   $165.3126   $165.31   $165.30   $165.30  
  Purchase #6 $32.47   5.556%   $34.274   $34.27   $34.25   $34.30  
  Purchase #7 $153.75   12.607%   $173.1333   $173.13   $173.15   $173.10  
  7 purchase totals = $582.14       $635.2340   $635.23   $635.25   $635.20