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 $86.69   13.389%   $98.2969   $98.30   $98.30   $98.30  
  Purchase #2 $188.72   3.610%   $195.5328   $195.53   $195.55   $195.50  
  Purchase #3 $210.72   13.384%   $238.9228   $238.92   $238.90   $238.90  
  Purchase #4 $28.46   7.734%   $30.6611   $30.66   $30.65   $30.70  
  Purchase #5 $204.44   3.564%   $211.7262   $211.73   $211.75   $211.70  
  Purchase #6 $17.78   6.352%   $18.9094   $18.91   $18.90   $18.90  
  Purchase #7 $219.47   9.192%   $239.6437   $239.64   $239.65   $239.60  
  7 purchase totals = $956.28       $1,033.6929   $1,033.69   $1,033.70   $1,033.60