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	$19.95	10.782%	$22.101	$22.10	$22.10	$22.10
Purchase #2	$242.34	5.740%	$256.2503	$256.25	$256.25	$256.30
Purchase #3	$25.82	9.717%	$28.3289	$28.33	$28.35	$28.30
Purchase #4	$199.53	8.783%	$217.0547	$217.05	$217.05	$217.10
Purchase #5	$106.70	12.300%	$119.8241	$119.82	$119.80	$119.80
Purchase #6	$225.27	5.720%	$238.1554	$238.16	$238.15	$238.20
Purchase #7	$154.74	11.515%	$172.5583	$172.56	$172.55	$172.60
7 purchase totals =	$974.35		$1,054.2727	$1,054.27	$1,054.25	$1,054.40