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 $59.78   3.701%   $61.9925   $61.99   $62.00   $62.00  
  Purchase #2 $35.48   10.795%   $39.3101   $39.31   $39.30   $39.30  
  Purchase #3 $172.45   7.838%   $185.9666   $185.97   $185.95   $186.00  
  Purchase #4 $216.92   5.129%   $228.0458   $228.05   $228.05   $228.00  
  Purchase #5 $103.29   13.598%   $117.3354   $117.34   $117.35   $117.30  
  Purchase #6 $158.50   4.515%   $165.6563   $165.66   $165.65   $165.70  
  Purchase #7 $62.37   3.472%   $64.5355   $64.54   $64.55   $64.50  
  7 purchase totals = $808.79       $862.8422   $862.86   $862.85   $862.80