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 $89.41   13.254%   $101.2604   $101.26   $101.25   $101.30  
  Purchase #2 $58.34   9.145%   $63.6752   $63.68   $63.70   $63.70  
  Purchase #3 $204.84   4.284%   $213.6153   $213.62   $213.60   $213.60  
  Purchase #4 $154.67   5.826%   $163.6811   $163.68   $163.70   $163.70  
  Purchase #5 $25.85   5.411%   $27.2487   $27.25   $27.25   $27.20  
  Purchase #6 $117.63   11.518%   $131.1786   $131.18   $131.20   $131.20  
  Purchase #7 $250.31   6.734%   $267.1659   $267.17   $267.15   $267.20  
  7 purchase totals = $901.05       $967.8252   $967.84   $967.85   $967.90