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	$230.33	5.114%	$242.1091	$242.11	$242.10	$242.10
Purchase #2	$140.86	11.564%	$157.1491	$157.15	$157.15	$157.10
Purchase #3	$205.56	11.820%	$229.8572	$229.86	$229.85	$229.90
Purchase #4	$99.29	3.188%	$102.4554	$102.46	$102.45	$102.50
Purchase #5	$17.71	4.238%	$18.4605	$18.46	$18.45	$18.50
Purchase #6	$234.71	4.409%	$245.0584	$245.06	$245.05	$245.10
Purchase #7	$218.31	12.479%	$245.5529	$245.55	$245.55	$245.60
7 purchase totals =	$1,146.77		$1,240.6426	$1,240.65	$1,240.60	$1,240.80