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 $97.68   6.654%   $104.1796   $104.18   $104.20   $104.20  
  Purchase #2 $222.30   7.223%   $238.3567   $238.36   $238.35   $238.40  
  Purchase #3 $159.64   4.259%   $166.4391   $166.44   $166.45   $166.40  
  Purchase #4 $207.75   13.612%   $236.0289   $236.03   $236.05   $236.00  
  Purchase #5 $132.73   8.347%   $143.809   $143.81   $143.80   $143.80  
  Purchase #6 $90.77   11.702%   $101.3919   $101.39   $101.40   $101.40  
  Purchase #7 $232.54   11.734%   $259.8262   $259.83   $259.85   $259.80  
  7 purchase totals = $1,143.41       $1,250.0314   $1,250.04   $1,250.10   $1,250.00