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	$150.86	3.707%	$156.4524	$156.45	$156.45	$156.50
Purchase #2	$53.55	4.656%	$56.0433	$56.04	$56.05	$56.00
Purchase #3	$146.55	4.374%	$152.9601	$152.96	$152.95	$153.00
Purchase #4	$91.41	3.374%	$94.4942	$94.49	$94.50	$94.50
Purchase #5	$35.95	4.352%	$37.5145	$37.51	$37.50	$37.50
Purchase #6	$131.69	5.693%	$139.1871	$139.19	$139.20	$139.20
Purchase #7	$193.74	13.683%	$220.2494	$220.25	$220.25	$220.20
7 purchase totals =	$803.75		$856.9010	$856.89	$856.90	$856.90