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 $216.96   11.436%   $241.7715   $241.77   $241.75   $241.80  
  Purchase #2 $63.83   10.687%   $70.6515   $70.65   $70.65   $70.70  
  Purchase #3 $236.46   8.116%   $255.6511   $255.65   $255.65   $255.70  
  Purchase #4 $66.96   8.226%   $72.4681   $72.47   $72.45   $72.50  
  Purchase #5 $65.47   11.552%   $73.0331   $73.03   $73.05   $73.00  
  Purchase #6 $66.69   11.386%   $74.2833   $74.28   $74.30   $74.30  
  Purchase #7 $228.70   9.278%   $249.9188   $249.92   $249.90   $249.90  
  7 purchase totals = $945.07       $1,037.7774   $1,037.77   $1,037.75   $1,037.90