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 $231.61   6.218%   $246.0115   $246.01   $246.00   $246.00  
  Purchase #2 $73.71   6.368%   $78.4039   $78.40   $78.40   $78.40  
  Purchase #3 $236.60   8.655%   $257.0777   $257.08   $257.10   $257.10  
  Purchase #4 $186.66   8.306%   $202.164   $202.16   $202.15   $202.20  
  Purchase #5 $185.53   3.626%   $192.2573   $192.26   $192.25   $192.30  
  Purchase #6 $41.97   12.698%   $47.2994   $47.30   $47.30   $47.30  
  Purchase #7 $195.86   8.826%   $213.1466   $213.15   $213.15   $213.10  
  7 purchase totals = $1,151.94       $1,236.3604   $1,236.36   $1,236.35   $1,236.40