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 $44.65   11.103%   $49.6075   $49.61   $49.60   $49.60  
  Purchase #2 $154.63   7.670%   $166.4901   $166.49   $166.50   $166.50  
  Purchase #3 $120.78   4.337%   $126.0182   $126.02   $126.00   $126.00  
  Purchase #4 $112.75   4.572%   $117.9049   $117.90   $117.90   $117.90  
  Purchase #5 $207.96   9.464%   $227.6413   $227.64   $227.65   $227.60  
  Purchase #6 $54.48   5.472%   $57.4611   $57.46   $57.45   $57.50  
  Purchase #7 $218.75   4.840%   $229.3375   $229.34   $229.35   $229.30  
  7 purchase totals = $914.00       $974.4606   $974.46   $974.45   $974.40