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	$16.84	10.850%	$18.6671	$18.67	$18.65	$18.70
Purchase #2	$30.34	5.861%	$32.1182	$32.12	$32.10	$32.10
Purchase #3	$90.37	4.140%	$94.1113	$94.11	$94.10	$94.10
Purchase #4	$193.92	3.178%	$200.0828	$200.08	$200.10	$200.10
Purchase #5	$104.45	5.565%	$110.2626	$110.26	$110.25	$110.30
Purchase #6	$57.91	10.782%	$64.1539	$64.15	$64.15	$64.20
Purchase #7	$142.88	3.813%	$148.328	$148.33	$148.35	$148.30
7 purchase totals =	$636.71		$667.7239	$667.72	$667.70	$667.80