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 $96.64   6.386%   $102.8114   $102.81   $102.80   $102.80  
  Purchase #2 $120.98   10.391%   $133.551   $133.55   $133.55   $133.60  
  Purchase #3 $244.44   6.386%   $260.0499   $260.05   $260.05   $260.00  
  Purchase #4 $234.26   11.384%   $260.9282   $260.93   $260.95   $260.90  
  Purchase #5 $192.78   3.139%   $198.8314   $198.83   $198.85   $198.80  
  Purchase #6 $43.26   10.872%   $47.9632   $47.96   $47.95   $48.00  
  Purchase #7 $30.71   11.504%   $34.2429   $34.24   $34.25   $34.20  
  7 purchase totals = $963.07       $1,038.3780   $1,038.37   $1,038.40   $1,038.30