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	$115.81	13.538%	$131.4884	$131.49	$131.50	$131.50
Purchase #2	$75.62	13.719%	$85.9943	$85.99	$86.00	$86.00
Purchase #3	$53.93	10.426%	$59.5527	$59.55	$59.55	$59.60
Purchase #4	$89.51	7.407%	$96.14	$96.14	$96.15	$96.10
Purchase #5	$151.82	12.734%	$171.1528	$171.15	$171.15	$171.20
Purchase #6	$48.75	12.442%	$54.8155	$54.82	$54.80	$54.80
Purchase #7	$237.60	8.706%	$258.2855	$258.29	$258.30	$258.30
7 purchase totals =	$773.04		$857.4292	$857.43	$857.45	$857.50