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	$37.42	13.626%	$42.5188	$42.52	$42.50	$42.50
Purchase #2	$231.37	4.481%	$241.7377	$241.74	$241.75	$241.70
Purchase #3	$25.90	9.437%	$28.3442	$28.34	$28.35	$28.30
Purchase #4	$72.54	10.671%	$80.2807	$80.28	$80.30	$80.30
Purchase #5	$86.68	10.523%	$95.8013	$95.80	$95.80	$95.80
Purchase #6	$221.51	8.494%	$240.3251	$240.33	$240.35	$240.30
Purchase #7	$90.60	6.305%	$96.3123	$96.31	$96.30	$96.30
7 purchase totals =	$766.02		$825.3201	$825.32	$825.35	$825.20