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	$121.32	4.842%	$127.1943	$127.19	$127.20	$127.20
Purchase #2	$47.50	6.263%	$50.4749	$50.47	$50.45	$50.50
Purchase #3	$120.34	5.540%	$127.0068	$127.01	$127.00	$127.00
Purchase #4	$88.75	11.699%	$99.1329	$99.13	$99.15	$99.10
Purchase #5	$70.76	13.710%	$80.4612	$80.46	$80.45	$80.50
Purchase #6	$228.92	10.465%	$252.8765	$252.88	$252.90	$252.90
Purchase #7	$86.33	11.818%	$96.5325	$96.53	$96.55	$96.50
7 purchase totals =	$763.92		$833.6791	$833.67	$833.70	$833.70