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 $23.95   4.458%   $25.0177   $25.02   $25.00   $25.00  
  Purchase #2 $237.93   11.377%   $264.9993   $265.00   $265.00   $265.00  
  Purchase #3 $107.36   9.410%   $117.4626   $117.46   $117.45   $117.50  
  Purchase #4 $13.36   12.864%   $15.0786   $15.08   $15.10   $15.10  
  Purchase #5 $238.93   6.260%   $253.887   $253.89   $253.90   $253.90  
  Purchase #6 $150.89   8.151%   $163.189   $163.19   $163.20   $163.20  
  Purchase #7 $235.27   5.779%   $248.8663   $248.87   $248.85   $248.90  
  7 purchase totals = $1,007.69       $1,088.5005   $1,088.51   $1,088.50   $1,088.60