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	$142.41	13.810%	$162.0768	$162.08	$162.10	$162.10
Purchase #2	$57.90	6.648%	$61.7492	$61.75	$61.75	$61.70
Purchase #3	$82.48	10.820%	$91.4043	$91.40	$91.40	$91.40
Purchase #4	$222.96	5.560%	$235.3566	$235.36	$235.35	$235.40
Purchase #5	$64.32	9.598%	$70.4934	$70.49	$70.50	$70.50
Purchase #6	$104.68	12.822%	$118.1021	$118.10	$118.10	$118.10
Purchase #7	$72.27	10.543%	$79.8894	$79.89	$79.90	$79.90
7 purchase totals =	$747.02		$819.0718	$819.07	$819.10	$819.10