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 $60.54   10.746%   $67.0456   $67.05   $67.05   $67.00  
  Purchase #2 $7.72   8.566%   $8.3813   $8.38   $8.40   $8.40  
  Purchase #3 $118.43   11.229%   $131.7285   $131.73   $131.75   $131.70  
  Purchase #4 $178.70   8.865%   $194.5418   $194.54   $194.55   $194.50  
  Purchase #5 $14.33   11.386%   $15.9616   $15.96   $15.95   $16.00  
  Purchase #6 $144.75   3.284%   $149.5036   $149.50   $149.50   $149.50  
  Purchase #7 $132.67   4.223%   $138.2727   $138.27   $138.25   $138.30  
  7 purchase totals = $657.14       $705.4351   $705.43   $705.45   $705.40