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	$50.71	7.164%	$54.3429	$54.34	$54.35	$54.30
Purchase #2	$207.32	6.323%	$220.4288	$220.43	$220.45	$220.40
Purchase #3	$51.45	3.463%	$53.2317	$53.23	$53.25	$53.20
Purchase #4	$103.54	9.708%	$113.5917	$113.59	$113.60	$113.60
Purchase #5	$56.64	13.682%	$64.3895	$64.39	$64.40	$64.40
Purchase #6	$35.38	13.413%	$40.1255	$40.13	$40.15	$40.10
Purchase #7	$64.33	9.731%	$70.59	$70.59	$70.60	$70.60
7 purchase totals =	$569.37		$616.7001	$616.70	$616.80	$616.60