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	$75.83	12.125%	$85.0244	$85.02	$85.00	$85.00
Purchase #2	$87.85	3.772%	$91.1637	$91.16	$91.15	$91.20
Purchase #3	$100.27	4.207%	$104.4884	$104.49	$104.50	$104.50
Purchase #4	$96.59	12.667%	$108.8251	$108.83	$108.85	$108.80
Purchase #5	$86.48	13.573%	$98.2179	$98.22	$98.20	$98.20
Purchase #6	$99.61	5.131%	$104.721	$104.72	$104.70	$104.70
Purchase #7	$97.98	9.456%	$107.245	$107.25	$107.25	$107.20
7 purchase totals =	$644.61		$699.6855	$699.69	$699.65	$699.60