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	$30.49	10.246%	$33.614	$33.61	$33.60	$33.60
Purchase #2	$135.48	13.777%	$154.1451	$154.15	$154.15	$154.10
Purchase #3	$106.39	4.792%	$111.4882	$111.49	$111.50	$111.50
Purchase #4	$33.99	3.706%	$35.2497	$35.25	$35.25	$35.20
Purchase #5	$47.63	13.138%	$53.8876	$53.89	$53.90	$53.90
Purchase #6	$97.43	4.262%	$101.5825	$101.58	$101.60	$101.60
Purchase #7	$241.74	3.797%	$250.9189	$250.92	$250.90	$250.90
7 purchase totals =	$693.15		$740.8860	$740.89	$740.90	$740.80