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	$138.42	4.625%	$144.8219	$144.82	$144.80	$144.80
Purchase #2	$175.91	6.568%	$187.4638	$187.46	$187.45	$187.50
Purchase #3	$199.72	13.728%	$227.1376	$227.14	$227.15	$227.10
Purchase #4	$119.85	9.840%	$131.6432	$131.64	$131.65	$131.60
Purchase #5	$49.62	11.703%	$55.427	$55.43	$55.45	$55.40
Purchase #6	$12.41	10.593%	$13.7246	$13.72	$13.70	$13.70
Purchase #7	$6.58	12.768%	$7.4201	$7.42	$7.40	$7.40
7 purchase totals =	$702.51		$767.6382	$767.63	$767.60	$767.50