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 $246.86   6.263%   $262.3208   $262.32   $262.30   $262.30  
  Purchase #2 $211.63   5.168%   $222.567   $222.57   $222.55   $222.60  
  Purchase #3 $75.66   10.171%   $83.3554   $83.36   $83.35   $83.40  
  Purchase #4 $226.62   8.376%   $245.6017   $245.60   $245.60   $245.60  
  Purchase #5 $210.53   3.311%   $217.5006   $217.50   $217.50   $217.50  
  Purchase #6 $182.69   7.715%   $196.7845   $196.78   $196.80   $196.80  
  Purchase #7 $26.40   10.204%   $29.0939   $29.09   $29.10   $29.10  
  7 purchase totals = $1,180.39       $1,257.2239   $1,257.22   $1,257.20   $1,257.30