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	$20.36	4.273%	$21.23	$21.23	$21.25	$21.20
Purchase #2	$91.91	10.421%	$101.4879	$101.49	$101.50	$101.50
Purchase #3	$74.31	11.629%	$82.9515	$82.95	$82.95	$83.00
Purchase #4	$24.72	4.548%	$25.8443	$25.84	$25.85	$25.80
Purchase #5	$147.89	7.825%	$159.4624	$159.46	$159.45	$159.50
Purchase #6	$236.53	5.284%	$249.0282	$249.03	$249.05	$249.00
Purchase #7	$152.59	12.803%	$172.1261	$172.13	$172.15	$172.10
7 purchase totals =	$748.31		$812.1304	$812.13	$812.20	$812.10