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 $88.72   7.521%   $95.3926   $95.39   $95.40   $95.40  
  Purchase #2 $97.48   5.269%   $102.6162   $102.62   $102.60   $102.60  
  Purchase #3 $209.52   11.365%   $233.3319   $233.33   $233.35   $233.30  
  Purchase #4 $91.67   5.115%   $96.3589   $96.36   $96.35   $96.40  
  Purchase #5 $29.67   3.561%   $30.7265   $30.73   $30.75   $30.70  
  Purchase #6 $98.33   3.215%   $101.4913   $101.49   $101.50   $101.50  
  Purchase #7 $250.67   11.306%   $279.0108   $279.01   $279.00   $279.00  
  7 purchase totals = $866.06       $938.9282   $938.93   $938.95   $938.90