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	$76.97	10.575%	$85.1096	$85.11	$85.10	$85.10
Purchase #2	$76.72	13.161%	$86.8171	$86.82	$86.80	$86.80
Purchase #3	$150.33	6.106%	$159.5091	$159.51	$159.50	$159.50
Purchase #4	$82.67	6.525%	$88.0642	$88.06	$88.05	$88.10
Purchase #5	$6.97	5.510%	$7.354	$7.35	$7.35	$7.40
Purchase #6	$204.74	5.168%	$215.321	$215.32	$215.30	$215.30
Purchase #7	$63.90	4.698%	$66.902	$66.90	$66.90	$66.90
7 purchase totals =	$662.30		$709.0770	$709.07	$709.00	$709.10