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	$85.41	6.178%	$90.6866	$90.69	$90.70	$90.70
Purchase #2	$225.78	5.772%	$238.812	$238.81	$238.80	$238.80
Purchase #3	$41.27	9.653%	$45.2538	$45.25	$45.25	$45.30
Purchase #4	$135.38	12.536%	$152.3512	$152.35	$152.35	$152.40
Purchase #5	$248.25	12.440%	$279.1323	$279.13	$279.15	$279.10
Purchase #6	$76.97	8.865%	$83.7934	$83.79	$83.80	$83.80
Purchase #7	$153.53	3.771%	$159.3196	$159.32	$159.30	$159.30
7 purchase totals =	$966.59		$1,049.3489	$1,049.34	$1,049.35	$1,049.40