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	$44.72	6.380%	$47.5731	$47.57	$47.55	$47.60
Purchase #2	$64.34	7.714%	$69.3032	$69.30	$69.30	$69.30
Purchase #3	$241.51	12.213%	$271.0056	$271.01	$271.00	$271.00
Purchase #4	$65.61	11.751%	$73.3198	$73.32	$73.30	$73.30
Purchase #5	$40.30	5.194%	$42.3932	$42.39	$42.40	$42.40
Purchase #6	$184.53	6.221%	$196.0096	$196.01	$196.00	$196.00
Purchase #7	$232.33	11.391%	$258.7947	$258.79	$258.80	$258.80
7 purchase totals =	$873.34		$958.3992	$958.39	$958.35	$958.40