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	$179.37	3.467%	$185.5888	$185.59	$185.60	$185.60
Purchase #2	$165.57	6.804%	$176.8354	$176.84	$176.85	$176.80
Purchase #3	$159.82	10.127%	$176.005	$176.01	$176.00	$176.00
Purchase #4	$18.57	6.870%	$19.8458	$19.85	$19.85	$19.80
Purchase #5	$242.45	3.172%	$250.1405	$250.14	$250.15	$250.10
Purchase #6	$48.72	10.802%	$53.9827	$53.98	$54.00	$54.00
Purchase #7	$26.99	6.755%	$28.8132	$28.81	$28.80	$28.80
7 purchase totals =	$841.49		$891.2114	$891.22	$891.25	$891.10