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 $220.46   13.861%   $251.018   $251.02   $251.00   $251.00  
  Purchase #2 $170.67   10.649%   $188.8446   $188.84   $188.85   $188.80  
  Purchase #3 $233.79   8.514%   $253.6949   $253.69   $253.70   $253.70  
  Purchase #4 $237.78   11.434%   $264.9678   $264.97   $264.95   $265.00  
  Purchase #5 $60.91   9.234%   $66.5344   $66.53   $66.55   $66.50  
  Purchase #6 $223.81   10.305%   $246.8736   $246.87   $246.85   $246.90  
  Purchase #7 $142.62   10.602%   $157.7406   $157.74   $157.75   $157.70  
  7 purchase totals = $1,290.04       $1,429.6739   $1,429.66   $1,429.65   $1,429.60