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	$157.74	4.360%	$164.6175	$164.62	$164.60	$164.60
Purchase #2	$111.82	10.510%	$123.5723	$123.57	$123.55	$123.60
Purchase #3	$96.83	9.409%	$105.9407	$105.94	$105.95	$105.90
Purchase #4	$155.27	11.421%	$173.0034	$173.00	$173.00	$173.00
Purchase #5	$67.82	9.640%	$74.3578	$74.36	$74.35	$74.40
Purchase #6	$191.89	6.402%	$204.1748	$204.17	$204.15	$204.20
Purchase #7	$76.61	4.615%	$80.1456	$80.15	$80.15	$80.10
7 purchase totals =	$857.98		$925.8121	$925.81	$925.75	$925.80