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 $57.60   13.282%   $65.2504   $65.25   $65.25   $65.30  
  Purchase #2 $45.64   5.131%   $47.9818   $47.98   $48.00   $48.00  
  Purchase #3 $15.52   9.480%   $16.9913   $16.99   $17.00   $17.00  
  Purchase #4 $62.74   6.868%   $67.049   $67.05   $67.05   $67.00  
  Purchase #5 $143.41   6.848%   $153.2307   $153.23   $153.25   $153.20  
  Purchase #6 $165.73   9.762%   $181.9086   $181.91   $181.90   $181.90  
  Purchase #7 $209.79   11.189%   $233.2634   $233.26   $233.25   $233.30  
  7 purchase totals = $700.43       $765.6752   $765.67   $765.70   $765.70