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	$136.82	8.281%	$148.1501	$148.15	$148.15	$148.20
Purchase #2	$167.44	10.630%	$185.2389	$185.24	$185.25	$185.20
Purchase #3	$223.34	5.789%	$236.2692	$236.27	$236.25	$236.30
Purchase #4	$70.47	7.823%	$75.9829	$75.98	$76.00	$76.00
Purchase #5	$244.90	12.650%	$275.8799	$275.88	$275.90	$275.90
Purchase #6	$101.65	12.762%	$114.6226	$114.62	$114.60	$114.60
Purchase #7	$236.95	11.634%	$264.5168	$264.52	$264.50	$264.50
7 purchase totals =	$1,181.57		$1,300.6604	$1,300.66	$1,300.65	$1,300.70