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	$50.28	8.200%	$54.403	$54.40	$54.40	$54.40
Purchase #2	$209.80	4.252%	$218.7207	$218.72	$218.70	$218.70
Purchase #3	$63.78	5.268%	$67.1399	$67.14	$67.15	$67.10
Purchase #4	$165.37	3.778%	$171.6177	$171.62	$171.60	$171.60
Purchase #5	$89.96	11.189%	$100.0256	$100.03	$100.05	$100.00
Purchase #6	$90.89	11.146%	$101.0206	$101.02	$101.00	$101.00
Purchase #7	$68.47	11.381%	$76.2626	$76.26	$76.25	$76.30
7 purchase totals =	$738.55		$789.1901	$789.19	$789.15	$789.10