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	$34.91	3.181%	$36.0205	$36.02	$36.00	$36.00
Purchase #2	$171.42	6.493%	$182.5503	$182.55	$182.55	$182.60
Purchase #3	$228.80	11.301%	$254.6567	$254.66	$254.65	$254.70
Purchase #4	$171.64	10.700%	$190.0055	$190.01	$190.00	$190.00
Purchase #5	$112.27	10.128%	$123.6407	$123.64	$123.65	$123.60
Purchase #6	$53.90	9.294%	$58.9095	$58.91	$58.90	$58.90
Purchase #7	$18.86	3.628%	$19.5442	$19.54	$19.55	$19.50
7 purchase totals =	$791.80		$865.3274	$865.33	$865.30	$865.30