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	$42.65	13.780%	$48.5272	$48.53	$48.55	$48.50
Purchase #2	$35.62	6.635%	$37.9834	$37.98	$38.00	$38.00
Purchase #3	$224.72	13.848%	$255.8392	$255.84	$255.85	$255.80
Purchase #4	$103.59	13.264%	$117.3302	$117.33	$117.35	$117.30
Purchase #5	$66.31	7.443%	$71.2455	$71.25	$71.25	$71.20
Purchase #6	$66.27	8.251%	$71.7379	$71.74	$71.75	$71.70
Purchase #7	$66.55	3.343%	$68.7748	$68.77	$68.75	$68.80
7 purchase totals =	$605.71		$671.4382	$671.44	$671.50	$671.30