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 $95.44   6.619%   $101.7572   $101.76   $101.75   $101.80  
  Purchase #2 $148.31   4.307%   $154.6977   $154.70   $154.70   $154.70  
  Purchase #3 $153.90   4.376%   $160.6347   $160.63   $160.65   $160.60  
  Purchase #4 $24.51   5.804%   $25.9326   $25.93   $25.95   $25.90  
  Purchase #5 $97.73   12.225%   $109.6775   $109.68   $109.70   $109.70  
  Purchase #6 $190.98   11.621%   $213.1738   $213.17   $213.15   $213.20  
  Purchase #7 $77.62   9.846%   $85.2625   $85.26   $85.25   $85.30  
  7 purchase totals = $788.49       $851.1360   $851.13   $851.15   $851.20