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	$248.59	10.826%	$275.5024	$275.50	$275.50	$275.50
Purchase #2	$71.63	8.118%	$77.4449	$77.44	$77.45	$77.40
Purchase #3	$169.64	11.540%	$189.2165	$189.22	$189.20	$189.20
Purchase #4	$233.52	13.382%	$264.7696	$264.77	$264.75	$264.80
Purchase #5	$215.88	3.528%	$223.4962	$223.50	$223.50	$223.50
Purchase #6	$76.68	12.479%	$86.2489	$86.25	$86.25	$86.20
Purchase #7	$118.44	7.440%	$127.2519	$127.25	$127.25	$127.30
7 purchase totals =	$1,134.38		$1,243.9304	$1,243.93	$1,243.90	$1,243.90