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	$80.85	11.365%	$90.0386	$90.04	$90.05	$90.00
Purchase #2	$123.44	6.157%	$131.0402	$131.04	$131.05	$131.00
Purchase #3	$152.28	13.383%	$172.6596	$172.66	$172.65	$172.70
Purchase #4	$42.81	10.114%	$47.1398	$47.14	$47.15	$47.10
Purchase #5	$37.91	4.228%	$39.5128	$39.51	$39.50	$39.50
Purchase #6	$72.58	10.664%	$80.3199	$80.32	$80.30	$80.30
Purchase #7	$199.66	8.669%	$216.9685	$216.97	$216.95	$217.00
7 purchase totals =	$709.53		$777.6794	$777.68	$777.65	$777.60