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 $47.96   4.191%   $49.97   $49.97   $49.95   $50.00  
  Purchase #2 $86.75   11.693%   $96.8937   $96.89   $96.90   $96.90  
  Purchase #3 $62.96   5.123%   $66.1854   $66.19   $66.20   $66.20  
  Purchase #4 $149.54   12.164%   $167.73   $167.73   $167.75   $167.70  
  Purchase #5 $223.81   7.632%   $240.8912   $240.89   $240.90   $240.90  
  Purchase #6 $55.77   5.414%   $58.7894   $58.79   $58.80   $58.80  
  Purchase #7 $154.28   9.440%   $168.844   $168.84   $168.85   $168.80  
  7 purchase totals = $781.07       $849.3037   $849.30   $849.35   $849.30