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	$19.34	13.165%	$21.8861	$21.89	$21.90	$21.90
Purchase #2	$158.77	7.783%	$171.1271	$171.13	$171.15	$171.10
Purchase #3	$240.90	5.191%	$253.4051	$253.41	$253.40	$253.40
Purchase #4	$138.56	10.767%	$153.4788	$153.48	$153.50	$153.50
Purchase #5	$144.35	8.705%	$156.9157	$156.92	$156.90	$156.90
Purchase #6	$68.57	5.734%	$72.5018	$72.50	$72.50	$72.50
Purchase #7	$43.28	13.281%	$49.028	$49.03	$49.05	$49.00
7 purchase totals =	$813.77		$878.3426	$878.36	$878.40	$878.30