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	$132.41	13.873%	$150.7792	$150.78	$150.80	$150.80
Purchase #2	$126.47	10.613%	$139.8923	$139.89	$139.90	$139.90
Purchase #3	$236.95	8.572%	$257.2614	$257.26	$257.25	$257.30
Purchase #4	$15.37	12.308%	$17.2617	$17.26	$17.25	$17.30
Purchase #5	$141.48	7.653%	$152.3075	$152.31	$152.30	$152.30
Purchase #6	$54.53	9.369%	$59.6389	$59.64	$59.65	$59.60
Purchase #7	$6.26	12.240%	$7.0262	$7.03	$7.05	$7.00
7 purchase totals =	$713.47		$784.1672	$784.17	$784.20	$784.20