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 $246.25   7.416%   $264.5119   $264.51   $264.50   $264.50  
  Purchase #2 $67.48   9.357%   $73.7941   $73.79   $73.80   $73.80  
  Purchase #3 $124.67   10.147%   $137.3203   $137.32   $137.30   $137.30  
  Purchase #4 $208.98   8.365%   $226.4612   $226.46   $226.45   $226.50  
  Purchase #5 $167.80   8.375%   $181.8533   $181.85   $181.85   $181.90  
  Purchase #6 $61.55   3.789%   $63.8821   $63.88   $63.90   $63.90  
  Purchase #7 $237.31   9.200%   $259.1425   $259.14   $259.15   $259.10  
  7 purchase totals = $1,114.04       $1,206.9654   $1,206.95   $1,206.95   $1,207.00