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	$190.94	11.617%	$213.1215	$213.12	$213.10	$213.10
Purchase #2	$90.48	6.530%	$96.3883	$96.39	$96.40	$96.40
Purchase #3	$73.99	8.575%	$80.3346	$80.33	$80.35	$80.30
Purchase #4	$52.38	10.476%	$57.8673	$57.87	$57.85	$57.90
Purchase #5	$70.88	7.599%	$76.2662	$76.27	$76.25	$76.30
Purchase #6	$105.62	6.660%	$112.6543	$112.65	$112.65	$112.70
Purchase #7	$40.30	6.335%	$42.853	$42.85	$42.85	$42.90
7 purchase totals =	$624.59		$679.4852	$679.48	$679.45	$679.60