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 $144.61   6.202%   $153.5787   $153.58   $153.60   $153.60  
  Purchase #2 $75.36   5.696%   $79.6525   $79.65   $79.65   $79.70  
  Purchase #3 $159.28   4.577%   $166.5702   $166.57   $166.55   $166.60  
  Purchase #4 $99.89   4.451%   $104.3361   $104.34   $104.35   $104.30  
  Purchase #5 $170.93   13.428%   $193.8825   $193.88   $193.90   $193.90  
  Purchase #6 $209.70   8.492%   $227.5077   $227.51   $227.50   $227.50  
  Purchase #7 $221.97   10.664%   $245.6409   $245.64   $245.65   $245.60  
  7 purchase totals = $1,081.74       $1,171.1686   $1,171.17   $1,171.20   $1,171.20