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 $185.58   11.369%   $206.6786   $206.68   $206.70   $206.70  
  Purchase #2 $215.96   9.522%   $236.5237   $236.52   $236.50   $236.50  
  Purchase #3 $87.96   4.396%   $91.8267   $91.83   $91.85   $91.80  
  Purchase #4 $49.44   5.167%   $51.9946   $51.99   $52.00   $52.00  
  Purchase #5 $226.53   13.287%   $256.629   $256.63   $256.65   $256.60  
  Purchase #6 $158.76   12.709%   $178.9368   $178.94   $178.95   $178.90  
  Purchase #7 $236.90   11.148%   $263.3096   $263.31   $263.30   $263.30  
  7 purchase totals = $1,161.13       $1,285.8990   $1,285.90   $1,285.95   $1,285.80