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	$218.65	12.623%	$246.2502	$246.25	$246.25	$246.30
Purchase #2	$65.69	13.106%	$74.2993	$74.30	$74.30	$74.30
Purchase #3	$225.87	13.138%	$255.5448	$255.54	$255.55	$255.50
Purchase #4	$125.88	11.814%	$140.7515	$140.75	$140.75	$140.80
Purchase #5	$42.75	5.514%	$45.1072	$45.11	$45.10	$45.10
Purchase #6	$143.69	5.318%	$151.3314	$151.33	$151.35	$151.30
Purchase #7	$77.89	3.824%	$80.8685	$80.87	$80.85	$80.90
7 purchase totals =	$900.42		$994.1529	$994.15	$994.15	$994.20