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	$77.90	6.238%	$82.7594	$82.76	$82.75	$82.80
Purchase #2	$147.42	12.838%	$166.3458	$166.35	$166.35	$166.30
Purchase #3	$76.87	11.222%	$85.4964	$85.50	$85.50	$85.50
Purchase #4	$152.85	10.487%	$168.8794	$168.88	$168.90	$168.90
Purchase #5	$140.56	4.276%	$146.5703	$146.57	$146.55	$146.60
Purchase #6	$17.86	10.245%	$19.6898	$19.69	$19.70	$19.70
Purchase #7	$180.44	7.436%	$193.8575	$193.86	$193.85	$193.90
7 purchase totals =	$793.90		$863.5986	$863.61	$863.60	$863.70