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 $187.70   9.532%   $205.5916   $205.59   $205.60   $205.60  
  Purchase #2 $117.51   12.824%   $132.5795   $132.58   $132.60   $132.60  
  Purchase #3 $236.39   3.556%   $244.796   $244.80   $244.80   $244.80  
  Purchase #4 $239.49   11.366%   $266.7104   $266.71   $266.70   $266.70  
  Purchase #5 $127.87   5.558%   $134.977   $134.98   $135.00   $135.00  
  Purchase #6 $49.83   8.124%   $53.8782   $53.88   $53.90   $53.90  
  Purchase #7 $15.36   9.872%   $16.8763   $16.88   $16.90   $16.90  
  7 purchase totals = $974.15       $1,055.4090   $1,055.42   $1,055.50   $1,055.50