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 $46.60   6.319%   $49.5447   $49.54   $49.55   $49.50  
  Purchase #2 $151.83   4.808%   $159.13   $159.13   $159.15   $159.10  
  Purchase #3 $50.26   5.373%   $52.9605   $52.96   $52.95   $53.00  
  Purchase #4 $35.72   3.547%   $36.987   $36.99   $37.00   $37.00  
  Purchase #5 $209.82   7.533%   $225.6257   $225.63   $225.65   $225.60  
  Purchase #6 $91.33   12.726%   $102.9527   $102.95   $102.95   $103.00  
  Purchase #7 $147.64   3.189%   $152.3482   $152.35   $152.35   $152.30  
  7 purchase totals = $733.20       $779.5488   $779.55   $779.60   $779.50