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	$165.69	12.453%	$186.3234	$186.32	$186.30	$186.30
Purchase #2	$183.72	3.126%	$189.4631	$189.46	$189.45	$189.50
Purchase #3	$34.64	7.482%	$37.2318	$37.23	$37.25	$37.20
Purchase #4	$74.78	6.457%	$79.6085	$79.61	$79.60	$79.60
Purchase #5	$171.82	3.205%	$177.3268	$177.33	$177.35	$177.30
Purchase #6	$98.90	12.729%	$111.489	$111.49	$111.50	$111.50
Purchase #7	$27.57	6.513%	$29.3656	$29.37	$29.35	$29.40
7 purchase totals =	$757.12		$810.8082	$810.81	$810.80	$810.80