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 $229.64   13.424%   $260.4669   $260.47   $260.45   $260.50  
  Purchase #2 $48.41   5.378%   $51.0135   $51.01   $51.00   $51.00  
  Purchase #3 $84.66   11.679%   $94.5474   $94.55   $94.55   $94.50  
  Purchase #4 $107.97   9.287%   $117.9972   $118.00   $118.00   $118.00  
  Purchase #5 $244.77   11.756%   $273.5452   $273.55   $273.55   $273.50  
  Purchase #6 $169.36   6.858%   $180.9747   $180.97   $180.95   $181.00  
  Purchase #7 $76.78   5.839%   $81.2632   $81.26   $81.25   $81.30  
  7 purchase totals = $961.59       $1,059.8081   $1,059.81   $1,059.75   $1,059.80