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 $58.97   10.725%   $65.2945   $65.29   $65.30   $65.30  
  Purchase #2 $217.95   7.673%   $234.6733   $234.67   $234.65   $234.70  
  Purchase #3 $142.97   7.220%   $153.2924   $153.29   $153.30   $153.30  
  Purchase #4 $6.76   8.597%   $7.3412   $7.34   $7.35   $7.30  
  Purchase #5 $37.42   8.776%   $40.704   $40.70   $40.70   $40.70  
  Purchase #6 $121.32   9.656%   $133.0347   $133.03   $133.05   $133.00  
  Purchase #7 $117.72   5.754%   $124.4936   $124.49   $124.50   $124.50  
  7 purchase totals = $703.11       $758.8337   $758.81   $758.85   $758.80