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	$31.52	6.115%	$33.4474	$33.45	$33.45	$33.40
Purchase #2	$135.34	12.769%	$152.6216	$152.62	$152.60	$152.60
Purchase #3	$172.71	4.869%	$181.1192	$181.12	$181.10	$181.10
Purchase #4	$37.79	3.346%	$39.0545	$39.05	$39.05	$39.10
Purchase #5	$55.69	5.436%	$58.7173	$58.72	$58.70	$58.70
Purchase #6	$64.83	7.764%	$69.8634	$69.86	$69.85	$69.90
Purchase #7	$116.99	10.114%	$128.8224	$128.82	$128.80	$128.80
7 purchase totals =	$614.87		$663.6458	$663.64	$663.55	$663.60