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 $207.93   3.423%   $215.0474   $215.05   $215.05   $215.00  
  Purchase #2 $235.43   6.592%   $250.9495   $250.95   $250.95   $250.90  
  Purchase #3 $206.86   4.443%   $216.0508   $216.05   $216.05   $216.10  
  Purchase #4 $95.48   5.248%   $100.4908   $100.49   $100.50   $100.50  
  Purchase #5 $235.29   7.337%   $252.5532   $252.55   $252.55   $252.60  
  Purchase #6 $196.52   10.545%   $217.243   $217.24   $217.25   $217.20  
  Purchase #7 $230.86   3.414%   $238.7416   $238.74   $238.75   $238.70  
  7 purchase totals = $1,408.37       $1,491.0763   $1,491.07   $1,491.10   $1,491.00