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 $228.43   5.660%   $241.3591   $241.36   $241.35   $241.40  
  Purchase #2 $185.55   4.562%   $194.0148   $194.01   $194.00   $194.00  
  Purchase #3 $107.36   11.542%   $119.7515   $119.75   $119.75   $119.80  
  Purchase #4 $84.62   6.236%   $89.8969   $89.90   $89.90   $89.90  
  Purchase #5 $212.90   13.216%   $241.0369   $241.04   $241.05   $241.00  
  Purchase #6 $85.36   4.195%   $88.9409   $88.94   $88.95   $88.90  
  Purchase #7 $207.95   13.506%   $236.0357   $236.04   $236.05   $236.00  
  7 purchase totals = $1,112.17       $1,211.0358   $1,211.04   $1,211.05   $1,211.00