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	$154.95	10.345%	$170.9796	$170.98	$171.00	$171.00
Purchase #2	$40.37	5.750%	$42.6913	$42.69	$42.70	$42.70
Purchase #3	$210.62	5.511%	$222.2273	$222.23	$222.25	$222.20
Purchase #4	$13.33	13.806%	$15.1703	$15.17	$15.15	$15.20
Purchase #5	$127.61	10.405%	$140.8878	$140.89	$140.90	$140.90
Purchase #6	$73.87	4.395%	$77.1166	$77.12	$77.10	$77.10
Purchase #7	$157.70	4.844%	$165.339	$165.34	$165.35	$165.30
7 purchase totals =	$778.45		$834.4119	$834.42	$834.45	$834.40