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	$109.41	12.332%	$122.9024	$122.90	$122.90	$122.90
Purchase #2	$232.41	4.399%	$242.6337	$242.63	$242.65	$242.60
Purchase #3	$22.98	3.180%	$23.7108	$23.71	$23.70	$23.70
Purchase #4	$38.73	9.738%	$42.5015	$42.50	$42.50	$42.50
Purchase #5	$55.91	5.775%	$59.1388	$59.14	$59.15	$59.10
Purchase #6	$235.70	12.346%	$264.7995	$264.80	$264.80	$264.80
Purchase #7	$101.46	9.820%	$111.4234	$111.42	$111.40	$111.40
7 purchase totals =	$796.60		$867.1101	$867.10	$867.10	$867.00