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 $229.85   7.752%   $247.668   $247.67   $247.65   $247.70  
  Purchase #2 $156.35   4.509%   $163.3998   $163.40   $163.40   $163.40  
  Purchase #3 $56.55   10.626%   $62.559   $62.56   $62.55   $62.60  
  Purchase #4 $69.88   5.616%   $73.8045   $73.80   $73.80   $73.80  
  Purchase #5 $15.28   4.135%   $15.9118   $15.91   $15.90   $15.90  
  Purchase #6 $209.86   5.474%   $221.3477   $221.35   $221.35   $221.30  
  Purchase #7 $211.69   11.480%   $235.992   $235.99   $236.00   $236.00  
  7 purchase totals = $949.46       $1,020.6828   $1,020.68   $1,020.65   $1,020.70