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	$95.83	10.125%	$105.5328	$105.53	$105.55	$105.50
Purchase #2	$211.32	11.426%	$235.4654	$235.47	$235.45	$235.50
Purchase #3	$65.92	7.731%	$71.0163	$71.02	$71.00	$71.00
Purchase #4	$81.88	4.184%	$85.3059	$85.31	$85.30	$85.30
Purchase #5	$30.34	13.188%	$34.3412	$34.34	$34.35	$34.30
Purchase #6	$96.85	11.815%	$108.2928	$108.29	$108.30	$108.30
Purchase #7	$17.71	3.347%	$18.3028	$18.30	$18.30	$18.30
7 purchase totals =	$599.85		$658.2572	$658.26	$658.25	$658.20