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 $43.64   13.815%   $49.6689   $49.67   $49.65   $49.70  
  Purchase #2 $209.52   10.504%   $231.528   $231.53   $231.55   $231.50  
  Purchase #3 $82.36   6.311%   $87.5577   $87.56   $87.55   $87.60  
  Purchase #4 $140.88   4.152%   $146.7293   $146.73   $146.75   $146.70  
  Purchase #5 $157.63   5.728%   $166.659   $166.66   $166.65   $166.70  
  Purchase #6 $148.27   3.575%   $153.5707   $153.57   $153.55   $153.60  
  Purchase #7 $67.69   11.492%   $75.4689   $75.47   $75.45   $75.50  
  7 purchase totals = $849.99       $911.1825   $911.19   $911.15   $911.30