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	$234.76	6.673%	$250.4255	$250.43	$250.45	$250.40
Purchase #2	$71.98	5.161%	$75.6949	$75.69	$75.70	$75.70
Purchase #3	$77.46	3.781%	$80.3888	$80.39	$80.40	$80.40
Purchase #4	$223.37	8.720%	$242.8479	$242.85	$242.85	$242.80
Purchase #5	$201.77	7.348%	$216.5961	$216.60	$216.60	$216.60
Purchase #6	$74.25	12.822%	$83.7703	$83.77	$83.75	$83.80
Purchase #7	$88.34	13.301%	$100.0901	$100.09	$100.10	$100.10
7 purchase totals =	$971.93		$1,049.8136	$1,049.82	$1,049.85	$1,049.80