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	$155.75	10.651%	$172.3389	$172.34	$172.35	$172.30
Purchase #2	$61.84	4.330%	$64.5177	$64.52	$64.50	$64.50
Purchase #3	$78.76	7.152%	$84.3929	$84.39	$84.40	$84.40
Purchase #4	$99.70	3.643%	$103.3321	$103.33	$103.35	$103.30
Purchase #5	$50.47	10.293%	$55.6649	$55.66	$55.65	$55.70
Purchase #6	$30.47	9.481%	$33.3589	$33.36	$33.35	$33.40
Purchase #7	$104.91	11.388%	$116.8572	$116.86	$116.85	$116.90
7 purchase totals =	$581.90		$630.4626	$630.46	$630.45	$630.50