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	$115.33	10.510%	$127.4512	$127.45	$127.45	$127.50
Purchase #2	$233.94	9.816%	$256.9036	$256.90	$256.90	$256.90
Purchase #3	$61.86	9.472%	$67.7194	$67.72	$67.70	$67.70
Purchase #4	$240.67	13.334%	$272.7609	$272.76	$272.75	$272.80
Purchase #5	$189.89	13.845%	$216.1803	$216.18	$216.20	$216.20
Purchase #6	$213.92	11.785%	$239.1305	$239.13	$239.15	$239.10
Purchase #7	$210.88	10.837%	$233.7331	$233.73	$233.75	$233.70
7 purchase totals =	$1,266.49		$1,413.8790	$1,413.87	$1,413.90	$1,413.90