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 $187.48   11.688%   $209.3927   $209.39   $209.40   $209.40  
  Purchase #2 $93.64   6.125%   $99.3755   $99.38   $99.40   $99.40  
  Purchase #3 $97.26   13.149%   $110.0487   $110.05   $110.05   $110.00  
  Purchase #4 $97.79   10.831%   $108.3816   $108.38   $108.40   $108.40  
  Purchase #5 $9.71   12.794%   $10.9523   $10.95   $10.95   $11.00  
  Purchase #6 $92.99   13.760%   $105.7854   $105.79   $105.80   $105.80  
  Purchase #7 $63.28   8.614%   $68.7309   $68.73   $68.75   $68.70  
  7 purchase totals = $642.15       $712.6671   $712.67   $712.75   $712.70