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 $234.77   4.564%   $245.4849   $245.48   $245.50   $245.50  
  Purchase #2 $183.27   7.302%   $196.6524   $196.65   $196.65   $196.70  
  Purchase #3 $160.73   5.381%   $169.3789   $169.38   $169.40   $169.40  
  Purchase #4 $171.76   3.839%   $178.3539   $178.35   $178.35   $178.40  
  Purchase #5 $136.84   12.145%   $153.4592   $153.46   $153.45   $153.50  
  Purchase #6 $18.74   3.618%   $19.418   $19.42   $19.40   $19.40  
  Purchase #7 $5.36   9.667%   $5.8782   $5.88   $5.90   $5.90  
  7 purchase totals = $911.47       $968.6255   $968.62   $968.65   $968.80