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	$248.44	9.123%	$271.1052	$271.11	$271.10	$271.10
Purchase #2	$110.83	11.487%	$123.561	$123.56	$123.55	$123.60
Purchase #3	$125.94	9.291%	$137.6411	$137.64	$137.65	$137.60
Purchase #4	$106.51	10.160%	$117.3314	$117.33	$117.35	$117.30
Purchase #5	$19.77	10.312%	$21.8087	$21.81	$21.80	$21.80
Purchase #6	$94.48	5.449%	$99.6282	$99.63	$99.65	$99.60
Purchase #7	$151.36	12.537%	$170.336	$170.34	$170.35	$170.30
7 purchase totals =	$857.33		$941.4116	$941.42	$941.45	$941.30