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	$49.85	5.593%	$52.6381	$52.64	$52.65	$52.60
Purchase #2	$192.79	7.526%	$207.2994	$207.30	$207.30	$207.30
Purchase #3	$108.84	13.593%	$123.6346	$123.63	$123.65	$123.60
Purchase #4	$230.84	9.779%	$253.4138	$253.41	$253.40	$253.40
Purchase #5	$140.57	11.363%	$156.543	$156.54	$156.55	$156.50
Purchase #6	$49.46	7.784%	$53.31	$53.31	$53.30	$53.30
Purchase #7	$68.41	4.510%	$71.4953	$71.50	$71.50	$71.50
7 purchase totals =	$840.76		$918.3342	$918.33	$918.35	$918.20