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 $97.84   6.594%   $104.2916   $104.29   $104.30   $104.30  
  Purchase #2 $202.99   10.742%   $224.7952   $224.80   $224.80   $224.80  
  Purchase #3 $165.91   3.263%   $171.3236   $171.32   $171.30   $171.30  
  Purchase #4 $140.53   13.521%   $159.5311   $159.53   $159.55   $159.50  
  Purchase #5 $123.83   6.825%   $132.2814   $132.28   $132.30   $132.30  
  Purchase #6 $34.67   5.786%   $36.676   $36.68   $36.70   $36.70  
  Purchase #7 $167.68   13.606%   $190.4945   $190.49   $190.50   $190.50  
  7 purchase totals = $933.45       $1,019.3934   $1,019.39   $1,019.45   $1,019.40