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	$31.37	3.162%	$32.3619	$32.36	$32.35	$32.40
Purchase #2	$173.37	3.309%	$179.1068	$179.11	$179.10	$179.10
Purchase #3	$243.66	6.145%	$258.6329	$258.63	$258.65	$258.60
Purchase #4	$101.70	11.761%	$113.6609	$113.66	$113.65	$113.70
Purchase #5	$183.40	3.198%	$189.2651	$189.27	$189.25	$189.30
Purchase #6	$79.78	8.807%	$86.8062	$86.81	$86.80	$86.80
Purchase #7	$75.49	9.246%	$82.4698	$82.47	$82.45	$82.50
7 purchase totals =	$888.77		$942.3036	$942.31	$942.25	$942.40