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 $233.95   11.616%   $261.1256   $261.13   $261.15   $261.10  
  Purchase #2 $159.75   13.775%   $181.7556   $181.76   $181.75   $181.80  
  Purchase #3 $5.56   12.768%   $6.2699   $6.27   $6.25   $6.30  
  Purchase #4 $90.69   5.785%   $95.9364   $95.94   $95.95   $95.90  
  Purchase #5 $200.93   5.489%   $211.959   $211.96   $211.95   $212.00  
  Purchase #6 $58.98   3.604%   $61.1056   $61.11   $61.10   $61.10  
  Purchase #7 $122.98   6.755%   $131.2873   $131.29   $131.30   $131.30  
  7 purchase totals = $872.84       $949.4394   $949.46   $949.45   $949.50