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	$130.79	13.409%	$148.3276	$148.33	$148.35	$148.30
Purchase #2	$108.93	3.247%	$112.467	$112.47	$112.45	$112.50
Purchase #3	$58.31	5.202%	$61.3433	$61.34	$61.35	$61.30
Purchase #4	$245.89	11.192%	$273.41	$273.41	$273.40	$273.40
Purchase #5	$130.85	4.114%	$136.2332	$136.23	$136.25	$136.20
Purchase #6	$47.28	7.180%	$50.6747	$50.67	$50.65	$50.70
Purchase #7	$103.84	7.635%	$111.7682	$111.77	$111.75	$111.80
7 purchase totals =	$825.89		$894.2240	$894.22	$894.20	$894.20