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	$45.98	8.668%	$49.9655	$49.97	$49.95	$50.00
Purchase #2	$50.30	10.521%	$55.5921	$55.59	$55.60	$55.60
Purchase #3	$121.58	12.131%	$136.3289	$136.33	$136.35	$136.30
Purchase #4	$219.58	5.497%	$231.6503	$231.65	$231.65	$231.70
Purchase #5	$94.63	11.438%	$105.4538	$105.45	$105.45	$105.50
Purchase #6	$94.83	4.786%	$99.3686	$99.37	$99.35	$99.40
Purchase #7	$44.69	11.800%	$49.9634	$49.96	$49.95	$50.00
7 purchase totals =	$671.59		$728.3226	$728.32	$728.30	$728.50