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 $38.37   8.596%   $41.6683   $41.67   $41.65   $41.70  
  Purchase #2 $88.58   8.868%   $96.4353   $96.44   $96.45   $96.40  
  Purchase #3 $93.26   9.215%   $101.8539   $101.85   $101.85   $101.90  
  Purchase #4 $215.72   11.215%   $239.913   $239.91   $239.90   $239.90  
  Purchase #5 $227.97   6.482%   $242.747   $242.75   $242.75   $242.70  
  Purchase #6 $163.87   10.136%   $180.4799   $180.48   $180.50   $180.50  
  Purchase #7 $95.28   8.785%   $103.6503   $103.65   $103.65   $103.70  
  7 purchase totals = $923.05       $1,006.7477   $1,006.75   $1,006.75   $1,006.80