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	$77.46	3.802%	$80.405	$80.41	$80.40	$80.40
Purchase #2	$132.37	3.576%	$137.1036	$137.10	$137.10	$137.10
Purchase #3	$104.52	10.560%	$115.5573	$115.56	$115.55	$115.60
Purchase #4	$135.90	5.489%	$143.3596	$143.36	$143.35	$143.40
Purchase #5	$31.72	10.761%	$35.1334	$35.13	$35.15	$35.10
Purchase #6	$33.94	3.478%	$35.1204	$35.12	$35.10	$35.10
Purchase #7	$34.65	13.278%	$39.2508	$39.25	$39.25	$39.30
7 purchase totals =	$550.56		$585.9301	$585.93	$585.90	$586.00