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	$179.72	10.433%	$198.4702	$198.47	$198.45	$198.50
Purchase #2	$52.98	11.600%	$59.1257	$59.13	$59.15	$59.10
Purchase #3	$140.36	7.443%	$150.807	$150.81	$150.80	$150.80
Purchase #4	$45.41	9.569%	$49.7553	$49.76	$49.75	$49.80
Purchase #5	$143.50	3.591%	$148.6531	$148.65	$148.65	$148.70
Purchase #6	$143.45	5.439%	$151.2522	$151.25	$151.25	$151.30
Purchase #7	$99.38	4.431%	$103.7835	$103.78	$103.80	$103.80
7 purchase totals =	$804.80		$861.8470	$861.85	$861.85	$862.00