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 $52.93   13.397%   $60.021   $60.02   $60.00   $60.00  
  Purchase #2 $74.41   3.238%   $76.8194   $76.82   $76.80   $76.80  
  Purchase #3 $125.81   12.350%   $141.3475   $141.35   $141.35   $141.30  
  Purchase #4 $72.67   3.456%   $75.1815   $75.18   $75.20   $75.20  
  Purchase #5 $66.67   5.355%   $70.2402   $70.24   $70.25   $70.20  
  Purchase #6 $185.62   4.646%   $194.2439   $194.24   $194.25   $194.20  
  Purchase #7 $129.93   13.597%   $147.5966   $147.60   $147.60   $147.60  
  7 purchase totals = $708.04       $765.4501   $765.45   $765.45   $765.30