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	$49.71	9.852%	$54.6074	$54.61	$54.60	$54.60
Purchase #2	$183.69	3.845%	$190.7529	$190.75	$190.75	$190.80
Purchase #3	$129.82	4.347%	$135.4633	$135.46	$135.45	$135.50
Purchase #4	$118.79	12.252%	$133.3442	$133.34	$133.35	$133.30
Purchase #5	$250.48	5.588%	$264.4768	$264.48	$264.50	$264.50
Purchase #6	$37.98	12.592%	$42.7624	$42.76	$42.75	$42.80
Purchase #7	$155.31	8.850%	$169.0549	$169.05	$169.05	$169.10
7 purchase totals =	$925.78		$990.4619	$990.45	$990.45	$990.60