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 $87.59   5.848%   $92.7123   $92.71   $92.70   $92.70  
  Purchase #2 $239.44   9.786%   $262.8716   $262.87   $262.85   $262.90  
  Purchase #3 $195.82   3.511%   $202.6952   $202.70   $202.70   $202.70  
  Purchase #4 $64.64   3.280%   $66.7602   $66.76   $66.75   $66.80  
  Purchase #5 $76.88   7.645%   $82.7575   $82.76   $82.75   $82.80  
  Purchase #6 $237.87   9.382%   $260.187   $260.19   $260.20   $260.20  
  Purchase #7 $48.32   3.622%   $50.0702   $50.07   $50.05   $50.10  
  7 purchase totals = $950.56       $1,018.0540   $1,018.06   $1,018.00   $1,018.20