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 $238.82   11.810%   $267.0246   $267.02   $267.00   $267.00  
  Purchase #2 $174.98   8.456%   $189.7763   $189.78   $189.80   $189.80  
  Purchase #3 $195.63   10.253%   $215.6879   $215.69   $215.70   $215.70  
  Purchase #4 $101.46   12.632%   $114.2764   $114.28   $114.30   $114.30  
  Purchase #5 $95.61   11.612%   $106.7122   $106.71   $106.70   $106.70  
  Purchase #6 $233.56   10.104%   $257.1589   $257.16   $257.15   $257.20  
  Purchase #7 $158.36   8.467%   $171.7683   $171.77   $171.75   $171.80  
  7 purchase totals = $1,198.42       $1,322.4046   $1,322.41   $1,322.40   $1,322.50