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 $189.61   5.796%   $200.5998   $200.60   $200.60   $200.60  
  Purchase #2 $233.44   6.204%   $247.9226   $247.92   $247.90   $247.90  
  Purchase #3 $168.68   9.505%   $184.713   $184.71   $184.70   $184.70  
  Purchase #4 $56.58   3.258%   $58.4234   $58.42   $58.40   $58.40  
  Purchase #5 $198.99   11.854%   $222.5783   $222.58   $222.60   $222.60  
  Purchase #6 $111.72   11.511%   $124.5801   $124.58   $124.60   $124.60  
  Purchase #7 $177.84   10.118%   $195.8339   $195.83   $195.85   $195.80  
  7 purchase totals = $1,136.86       $1,234.6511   $1,234.64   $1,234.65   $1,234.60