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 $62.55   6.639%   $66.7027   $66.70   $66.70   $66.70  
  Purchase #2 $244.77   4.256%   $255.1874   $255.19   $255.20   $255.20  
  Purchase #3 $13.54   5.862%   $14.3337   $14.33   $14.35   $14.30  
  Purchase #4 $38.99   6.228%   $41.4183   $41.42   $41.40   $41.40  
  Purchase #5 $173.74   5.783%   $183.7874   $183.79   $183.80   $183.80  
  Purchase #6 $93.28   4.418%   $97.4011   $97.40   $97.40   $97.40  
  Purchase #7 $91.71   4.526%   $95.8608   $95.86   $95.85   $95.90  
  7 purchase totals = $718.58       $754.6914   $754.69   $754.70   $754.70