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	$77.41	5.650%	$81.7837	$81.78	$81.80	$81.80
Purchase #2	$117.88	8.430%	$127.8173	$127.82	$127.80	$127.80
Purchase #3	$199.70	12.815%	$225.2916	$225.29	$225.30	$225.30
Purchase #4	$152.27	13.303%	$172.5265	$172.53	$172.55	$172.50
Purchase #5	$246.70	8.435%	$267.5091	$267.51	$267.50	$267.50
Purchase #6	$133.52	5.717%	$141.1533	$141.15	$141.15	$141.20
Purchase #7	$214.90	5.544%	$226.8141	$226.81	$226.80	$226.80
7 purchase totals =	$1,142.38		$1,242.8956	$1,242.89	$1,242.90	$1,242.90