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 $205.29   5.206%   $215.9774   $215.98   $216.00   $216.00  
  Purchase #2 $240.82   11.356%   $268.1675   $268.17   $268.15   $268.20  
  Purchase #3 $188.66   10.732%   $208.907   $208.91   $208.90   $208.90  
  Purchase #4 $122.98   10.253%   $135.5891   $135.59   $135.60   $135.60  
  Purchase #5 $136.91   10.443%   $151.2075   $151.21   $151.20   $151.20  
  Purchase #6 $238.93   3.161%   $246.4826   $246.48   $246.50   $246.50  
  Purchase #7 $103.81   3.531%   $107.4755   $107.48   $107.50   $107.50  
  7 purchase totals = $1,237.40       $1,333.8066   $1,333.82   $1,333.85   $1,333.90