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 $56.63   12.374%   $63.6374   $63.64   $63.65   $63.60  
  Purchase #2 $233.48   12.594%   $262.8845   $262.88   $262.90   $262.90  
  Purchase #3 $46.76   10.257%   $51.5562   $51.56   $51.55   $51.60  
  Purchase #4 $214.62   10.565%   $237.2946   $237.29   $237.30   $237.30  
  Purchase #5 $48.81   8.729%   $53.0706   $53.07   $53.05   $53.10  
  Purchase #6 $74.40   7.816%   $80.2151   $80.22   $80.20   $80.20  
  Purchase #7 $234.89   13.385%   $266.33   $266.33   $266.35   $266.30  
  7 purchase totals = $909.59       $1,014.9884   $1,014.99   $1,015.00   $1,015.00