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	$28.83	12.812%	$32.5237	$32.52	$32.50	$32.50
Purchase #2	$161.44	4.363%	$168.4836	$168.48	$168.50	$168.50
Purchase #3	$26.42	4.833%	$27.6969	$27.70	$27.70	$27.70
Purchase #4	$192.32	4.485%	$200.9456	$200.95	$200.95	$200.90
Purchase #5	$92.49	7.609%	$99.5276	$99.53	$99.55	$99.50
Purchase #6	$63.32	13.198%	$71.677	$71.68	$71.70	$71.70
Purchase #7	$88.50	7.824%	$95.4242	$95.42	$95.40	$95.40
7 purchase totals =	$653.32		$696.2786	$696.28	$696.30	$696.20