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 $92.79   9.538%   $101.6403   $101.64   $101.65   $101.60  
  Purchase #2 $62.82   7.643%   $67.6213   $67.62   $67.60   $67.60  
  Purchase #3 $213.63   11.135%   $237.4177   $237.42   $237.40   $237.40  
  Purchase #4 $55.26   4.240%   $57.603   $57.60   $57.60   $57.60  
  Purchase #5 $56.90   7.563%   $61.2033   $61.20   $61.20   $61.20  
  Purchase #6 $95.85   12.438%   $107.7718   $107.77   $107.75   $107.80  
  Purchase #7 $124.58   4.345%   $129.993   $129.99   $130.00   $130.00  
  7 purchase totals = $701.83       $763.2504   $763.24   $763.20   $763.20