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 $233.83   7.633%   $251.6782   $251.68   $251.70   $251.70  
  Purchase #2 $117.81   6.252%   $125.1755   $125.18   $125.20   $125.20  
  Purchase #3 $32.53   5.356%   $34.2723   $34.27   $34.25   $34.30  
  Purchase #4 $59.85   3.636%   $62.0261   $62.03   $62.05   $62.00  
  Purchase #5 $165.46   7.678%   $178.164   $178.16   $178.15   $178.20  
  Purchase #6 $148.84   4.749%   $155.9084   $155.91   $155.90   $155.90  
  Purchase #7 $136.88   10.125%   $150.7391   $150.74   $150.75   $150.70  
  7 purchase totals = $895.20       $957.9636   $957.97   $958.00   $958.00