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 $55.51   11.311%   $61.7887   $61.79   $61.80   $61.80  
  Purchase #2 $166.50   10.316%   $183.6761   $183.68   $183.70   $183.70  
  Purchase #3 $70.35   8.454%   $76.2974   $76.30   $76.30   $76.30  
  Purchase #4 $219.75   10.412%   $242.6304   $242.63   $242.65   $242.60  
  Purchase #5 $48.58   5.537%   $51.2699   $51.27   $51.25   $51.30  
  Purchase #6 $78.43   6.466%   $83.5013   $83.50   $83.50   $83.50  
  Purchase #7 $236.94   8.747%   $257.6651   $257.67   $257.65   $257.70  
  7 purchase totals = $876.06       $956.8289   $956.84   $956.85   $956.90