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	$167.99	9.720%	$184.3186	$184.32	$184.30	$184.30
Purchase #2	$186.40	7.453%	$200.2924	$200.29	$200.30	$200.30
Purchase #3	$49.90	11.502%	$55.6395	$55.64	$55.65	$55.60
Purchase #4	$71.25	10.291%	$78.5823	$78.58	$78.60	$78.60
Purchase #5	$215.82	13.175%	$244.2543	$244.25	$244.25	$244.30
Purchase #6	$100.85	11.216%	$112.1613	$112.16	$112.15	$112.20
Purchase #7	$102.34	12.685%	$115.3218	$115.32	$115.30	$115.30
7 purchase totals =	$894.55		$990.5702	$990.56	$990.55	$990.60