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	$98.87	10.707%	$109.456	$109.46	$109.45	$109.50
Purchase #2	$214.44	7.862%	$231.2993	$231.30	$231.30	$231.30
Purchase #3	$112.54	5.546%	$118.7815	$118.78	$118.80	$118.80
Purchase #4	$37.78	11.478%	$42.1164	$42.12	$42.10	$42.10
Purchase #5	$76.81	3.367%	$79.3962	$79.40	$79.40	$79.40
Purchase #6	$78.31	13.819%	$89.1317	$89.13	$89.15	$89.10
Purchase #7	$233.85	6.740%	$249.6115	$249.61	$249.60	$249.60
7 purchase totals =	$852.60		$919.7926	$919.80	$919.80	$919.80