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	$220.69	4.169%	$229.8906	$229.89	$229.90	$229.90
Purchase #2	$16.83	7.290%	$18.0569	$18.06	$18.05	$18.10
Purchase #3	$171.25	12.263%	$192.2504	$192.25	$192.25	$192.30
Purchase #4	$31.48	6.418%	$33.5004	$33.50	$33.50	$33.50
Purchase #5	$89.89	8.168%	$97.2322	$97.23	$97.25	$97.20
Purchase #6	$87.80	9.761%	$96.3702	$96.37	$96.35	$96.40
Purchase #7	$66.76	10.247%	$73.6009	$73.60	$73.60	$73.60
7 purchase totals =	$684.70		$740.9016	$740.90	$740.90	$741.00