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	$37.89	5.104%	$39.8239	$39.82	$39.80	$39.80
Purchase #2	$72.66	10.753%	$80.4731	$80.47	$80.45	$80.50
Purchase #3	$132.28	11.647%	$147.6867	$147.69	$147.70	$147.70
Purchase #4	$86.99	11.327%	$96.8434	$96.84	$96.85	$96.80
Purchase #5	$135.70	4.436%	$141.7197	$141.72	$141.70	$141.70
Purchase #6	$64.28	13.396%	$72.8909	$72.89	$72.90	$72.90
Purchase #7	$15.53	12.642%	$17.4933	$17.49	$17.50	$17.50
7 purchase totals =	$545.33		$596.9310	$596.92	$596.90	$596.90