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 $38.93   4.658%   $40.7434   $40.74   $40.75   $40.70  
  Purchase #2 $167.74   11.266%   $186.6376   $186.64   $186.65   $186.60  
  Purchase #3 $115.65   3.338%   $119.5104   $119.51   $119.50   $119.50  
  Purchase #4 $75.71   6.524%   $80.6493   $80.65   $80.65   $80.60  
  Purchase #5 $73.52   4.316%   $76.6931   $76.69   $76.70   $76.70  
  Purchase #6 $215.48   5.552%   $227.4434   $227.44   $227.45   $227.40  
  Purchase #7 $84.59   10.478%   $93.4533   $93.45   $93.45   $93.50  
  7 purchase totals = $771.62       $825.1305   $825.12   $825.15   $825.00