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 $67.97   8.127%   $73.4939   $73.49   $73.50   $73.50  
  Purchase #2 $55.70   12.554%   $62.6926   $62.69   $62.70   $62.70  
  Purchase #3 $150.99   7.302%   $162.0153   $162.02   $162.00   $162.00  
  Purchase #4 $219.44   3.767%   $227.7063   $227.71   $227.70   $227.70  
  Purchase #5 $18.64   13.420%   $21.1415   $21.14   $21.15   $21.10  
  Purchase #6 $151.89   7.522%   $163.3152   $163.32   $163.30   $163.30  
  Purchase #7 $234.48   7.463%   $251.9792   $251.98   $252.00   $252.00  
  7 purchase totals = $899.11       $962.3440   $962.35   $962.35   $962.30