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 $121.86   11.246%   $135.5644   $135.56   $135.55   $135.60  
  Purchase #2 $77.90   7.357%   $83.6311   $83.63   $83.65   $83.60  
  Purchase #3 $46.38   11.582%   $51.7517   $51.75   $51.75   $51.80  
  Purchase #4 $110.73   5.832%   $117.1878   $117.19   $117.20   $117.20  
  Purchase #5 $217.67   5.419%   $229.4655   $229.47   $229.45   $229.50  
  Purchase #6 $109.64   6.546%   $116.817   $116.82   $116.80   $116.80  
  Purchase #7 $219.55   3.601%   $227.456   $227.46   $227.45   $227.50  
  7 purchase totals = $903.73       $961.8735   $961.88   $961.85   $962.00