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	$141.99	12.267%	$159.4079	$159.41	$159.40	$159.40
Purchase #2	$102.33	3.470%	$105.8809	$105.88	$105.90	$105.90
Purchase #3	$89.63	12.118%	$100.4914	$100.49	$100.50	$100.50
Purchase #4	$39.47	9.256%	$43.1233	$43.12	$43.10	$43.10
Purchase #5	$162.50	6.812%	$173.5695	$173.57	$173.55	$173.60
Purchase #6	$178.39	4.227%	$185.9305	$185.93	$185.95	$185.90
Purchase #7	$109.25	5.675%	$115.4499	$115.45	$115.45	$115.40
7 purchase totals =	$823.56		$883.8534	$883.85	$883.85	$883.80