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	$247.38	12.789%	$279.0174	$279.02	$279.00	$279.00
Purchase #2	$187.78	4.600%	$196.4179	$196.42	$196.40	$196.40
Purchase #3	$31.87	10.699%	$35.2798	$35.28	$35.30	$35.30
Purchase #4	$176.50	8.365%	$191.2642	$191.26	$191.25	$191.30
Purchase #5	$69.77	12.447%	$78.4543	$78.45	$78.45	$78.50
Purchase #6	$193.48	6.740%	$206.5206	$206.52	$206.50	$206.50
Purchase #7	$183.40	9.281%	$200.4214	$200.42	$200.40	$200.40
7 purchase totals =	$1,090.18		$1,187.3756	$1,187.37	$1,187.30	$1,187.40