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 $246.78   8.561%   $267.9068   $267.91   $267.90   $267.90  
  Purchase #2 $142.81   5.570%   $150.7645   $150.76   $150.75   $150.80  
  Purchase #3 $245.71   6.607%   $261.9441   $261.94   $261.95   $261.90  
  Purchase #4 $224.98   12.606%   $253.341   $253.34   $253.35   $253.30  
  Purchase #5 $140.77   12.689%   $158.6323   $158.63   $158.65   $158.60  
  Purchase #6 $92.42   3.859%   $95.9865   $95.99   $96.00   $96.00  
  Purchase #7 $102.79   3.534%   $106.4226   $106.42   $106.40   $106.40  
  7 purchase totals = $1,196.26       $1,294.9978   $1,294.99   $1,295.00   $1,294.90