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 $133.46   13.462%   $151.4264   $151.43   $151.45   $151.40  
  Purchase #2 $179.85   7.860%   $193.9862   $193.99   $194.00   $194.00  
  Purchase #3 $226.86   5.126%   $238.4888   $238.49   $238.50   $238.50  
  Purchase #4 $207.80   3.277%   $214.6096   $214.61   $214.60   $214.60  
  Purchase #5 $10.46   7.146%   $11.2075   $11.21   $11.20   $11.20  
  Purchase #6 $148.93   9.531%   $163.1245   $163.12   $163.10   $163.10  
  Purchase #7 $92.42   6.506%   $98.4328   $98.43   $98.45   $98.40  
  7 purchase totals = $999.78       $1,071.2758   $1,071.28   $1,071.30   $1,071.20