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 $184.66   10.363%   $203.7963   $203.80   $203.80   $203.80  
  Purchase #2 $244.85   12.313%   $274.9984   $275.00   $275.00   $275.00  
  Purchase #3 $79.91   3.174%   $82.4463   $82.45   $82.45   $82.40  
  Purchase #4 $23.71   5.688%   $25.0586   $25.06   $25.05   $25.10  
  Purchase #5 $39.99   4.805%   $41.9115   $41.91   $41.90   $41.90  
  Purchase #6 $17.37   10.360%   $19.1695   $19.17   $19.15   $19.20  
  Purchase #7 $249.44   4.628%   $260.9841   $260.98   $261.00   $261.00  
  7 purchase totals = $839.93       $908.3647   $908.37   $908.35   $908.40