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	$223.79	11.843%	$250.2934	$250.29	$250.30	$250.30
Purchase #2	$99.91	5.439%	$105.3441	$105.34	$105.35	$105.30
Purchase #3	$40.29	11.743%	$45.0213	$45.02	$45.00	$45.00
Purchase #4	$33.94	3.453%	$35.1119	$35.11	$35.10	$35.10
Purchase #5	$120.90	5.641%	$127.72	$127.72	$127.70	$127.70
Purchase #6	$14.91	11.156%	$16.5734	$16.57	$16.55	$16.60
Purchase #7	$38.98	3.801%	$40.4616	$40.46	$40.45	$40.50
7 purchase totals =	$572.72		$620.5257	$620.51	$620.45	$620.50