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 $126.81   4.171%   $132.0992   $132.10   $132.10   $132.10  
  Purchase #2 $208.94   8.155%   $225.9791   $225.98   $226.00   $226.00  
  Purchase #3 $49.64   13.347%   $56.2655   $56.27   $56.25   $56.30  
  Purchase #4 $199.74   10.788%   $221.288   $221.29   $221.30   $221.30  
  Purchase #5 $22.33   6.163%   $23.7062   $23.71   $23.70   $23.70  
  Purchase #6 $245.57   13.323%   $278.2873   $278.29   $278.30   $278.30  
  Purchase #7 $19.92   7.643%   $21.4425   $21.44   $21.45   $21.40  
  7 purchase totals = $872.95       $959.0678   $959.08   $959.10   $959.10