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 $42.58   11.641%   $47.5367   $47.54   $47.55   $47.50  
  Purchase #2 $228.25   8.635%   $247.9594   $247.96   $247.95   $248.00  
  Purchase #3 $163.73   12.826%   $184.73   $184.73   $184.75   $184.70  
  Purchase #4 $70.97   6.509%   $75.5894   $75.59   $75.60   $75.60  
  Purchase #5 $222.71   10.413%   $245.9008   $245.90   $245.90   $245.90  
  Purchase #6 $216.36   13.714%   $246.0316   $246.03   $246.05   $246.00  
  Purchase #7 $141.60   13.131%   $160.1935   $160.19   $160.20   $160.20  
  7 purchase totals = $1,086.20       $1,207.9414   $1,207.94   $1,208.00   $1,207.90