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	$150.97	6.148%	$160.2516	$160.25	$160.25	$160.30
Purchase #2	$198.41	3.268%	$204.894	$204.89	$204.90	$204.90
Purchase #3	$153.61	11.530%	$171.3212	$171.32	$171.30	$171.30
Purchase #4	$171.94	8.148%	$185.9497	$185.95	$185.95	$185.90
Purchase #5	$153.98	11.334%	$171.4321	$171.43	$171.45	$171.40
Purchase #6	$87.87	12.709%	$99.0374	$99.04	$99.05	$99.00
Purchase #7	$184.53	12.473%	$207.5464	$207.55	$207.55	$207.50
7 purchase totals =	$1,101.31		$1,200.4324	$1,200.43	$1,200.45	$1,200.30