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	$136.36	13.830%	$155.2186	$155.22	$155.20	$155.20
Purchase #2	$159.38	7.731%	$171.7017	$171.70	$171.70	$171.70
Purchase #3	$189.81	11.554%	$211.7406	$211.74	$211.75	$211.70
Purchase #4	$197.95	5.149%	$208.1424	$208.14	$208.15	$208.10
Purchase #5	$40.94	4.812%	$42.91	$42.91	$42.90	$42.90
Purchase #6	$103.53	7.284%	$111.0711	$111.07	$111.05	$111.10
Purchase #7	$96.85	9.231%	$105.7902	$105.79	$105.80	$105.80
7 purchase totals =	$924.82		$1,006.5746	$1,006.57	$1,006.55	$1,006.50