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	$83.90	6.826%	$89.627	$89.63	$89.65	$89.60
Purchase #2	$149.80	6.152%	$159.0157	$159.02	$159.00	$159.00
Purchase #3	$37.60	8.761%	$40.8941	$40.89	$40.90	$40.90
Purchase #4	$137.86	8.317%	$149.3258	$149.33	$149.35	$149.30
Purchase #5	$162.47	5.784%	$171.8673	$171.87	$171.85	$171.90
Purchase #6	$186.64	3.307%	$192.8122	$192.81	$192.80	$192.80
Purchase #7	$86.70	12.253%	$97.3234	$97.32	$97.30	$97.30
7 purchase totals =	$844.97		$900.8655	$900.87	$900.85	$900.80