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	$74.91	11.114%	$83.2355	$83.24	$83.25	$83.20
Purchase #2	$249.86	5.399%	$263.3499	$263.35	$263.35	$263.30
Purchase #3	$141.84	9.590%	$155.4425	$155.44	$155.45	$155.40
Purchase #4	$46.84	13.437%	$53.1339	$53.13	$53.15	$53.10
Purchase #5	$209.28	6.299%	$222.4625	$222.46	$222.45	$222.50
Purchase #6	$178.30	7.448%	$191.5798	$191.58	$191.60	$191.60
Purchase #7	$92.31	13.121%	$104.422	$104.42	$104.40	$104.40
7 purchase totals =	$993.34		$1,073.6261	$1,073.62	$1,073.65	$1,073.50