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 $146.54   5.117%   $154.0385   $154.04   $154.05   $154.00  
  Purchase #2 $81.41   8.140%   $88.0368   $88.04   $88.05   $88.00  
  Purchase #3 $201.75   7.505%   $216.8913   $216.89   $216.90   $216.90  
  Purchase #4 $24.99   5.372%   $26.3325   $26.33   $26.35   $26.30  
  Purchase #5 $66.65   5.509%   $70.3217   $70.32   $70.30   $70.30  
  Purchase #6 $236.93   10.347%   $261.4451   $261.45   $261.45   $261.40  
  Purchase #7 $117.29   12.750%   $132.2445   $132.24   $132.25   $132.20  
  7 purchase totals = $875.56       $949.3104   $949.31   $949.35   $949.10