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 $237.43   4.163%   $247.3142   $247.31   $247.30   $247.30  
  Purchase #2 $154.87   4.599%   $161.9925   $161.99   $162.00   $162.00  
  Purchase #3 $97.91   10.854%   $108.5372   $108.54   $108.55   $108.50  
  Purchase #4 $246.47   5.765%   $260.679   $260.68   $260.70   $260.70  
  Purchase #5 $165.74   12.145%   $185.8691   $185.87   $185.85   $185.90  
  Purchase #6 $174.78   9.407%   $191.2216   $191.22   $191.20   $191.20  
  Purchase #7 $76.30   10.337%   $84.1871   $84.19   $84.20   $84.20  
  7 purchase totals = $1,153.50       $1,239.8007   $1,239.80   $1,239.80   $1,239.80