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	$76.27	6.146%	$80.9576	$80.96	$80.95	$81.00
Purchase #2	$5.74	9.272%	$6.2722	$6.27	$6.25	$6.30
Purchase #3	$32.39	13.545%	$36.7772	$36.78	$36.80	$36.80
Purchase #4	$122.39	9.859%	$134.4564	$134.46	$134.45	$134.50
Purchase #5	$79.46	12.594%	$89.4672	$89.47	$89.45	$89.50
Purchase #6	$180.54	10.303%	$199.141	$199.14	$199.15	$199.10
Purchase #7	$33.41	6.198%	$35.4808	$35.48	$35.50	$35.50
7 purchase totals =	$530.20		$582.5524	$582.56	$582.55	$582.70