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 $151.72   3.205%   $156.5826   $156.58   $156.60   $156.60  
  Purchase #2 $223.53   13.137%   $252.8951   $252.90   $252.90   $252.90  
  Purchase #3 $244.56   3.842%   $253.956   $253.96   $253.95   $254.00  
  Purchase #4 $8.38   6.107%   $8.8918   $8.89   $8.90   $8.90  
  Purchase #5 $53.86   12.577%   $60.634   $60.63   $60.65   $60.60  
  Purchase #6 $50.49   11.866%   $56.4811   $56.48   $56.50   $56.50  
  Purchase #7 $31.27   10.359%   $34.5093   $34.51   $34.50   $34.50  
  7 purchase totals = $763.81       $823.9499   $823.95   $824.00   $824.00