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	$88.44	3.479%	$91.5168	$91.52	$91.50	$91.50
Purchase #2	$111.55	11.476%	$124.3515	$124.35	$124.35	$124.40
Purchase #3	$43.75	3.215%	$45.1566	$45.16	$45.15	$45.20
Purchase #4	$200.59	7.858%	$216.3524	$216.35	$216.35	$216.40
Purchase #5	$77.58	10.604%	$85.8066	$85.81	$85.80	$85.80
Purchase #6	$145.32	10.397%	$160.4289	$160.43	$160.45	$160.40
Purchase #7	$86.60	10.348%	$95.5614	$95.56	$95.55	$95.60
7 purchase totals =	$753.83		$819.1742	$819.18	$819.15	$819.30