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	$75.36	11.809%	$84.2593	$84.26	$84.25	$84.30
Purchase #2	$174.52	12.839%	$196.9266	$196.93	$196.95	$196.90
Purchase #3	$49.60	5.164%	$52.1613	$52.16	$52.15	$52.20
Purchase #4	$42.58	12.793%	$48.0273	$48.03	$48.05	$48.00
Purchase #5	$65.87	9.506%	$72.1316	$72.13	$72.15	$72.10
Purchase #6	$216.73	12.251%	$243.2816	$243.28	$243.30	$243.30
Purchase #7	$245.46	10.694%	$271.7095	$271.71	$271.70	$271.70
7 purchase totals =	$870.12		$968.4972	$968.50	$968.55	$968.50