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	$140.92	13.231%	$159.5651	$159.57	$159.55	$159.60
Purchase #2	$155.98	9.535%	$170.8527	$170.85	$170.85	$170.90
Purchase #3	$31.52	12.581%	$35.4855	$35.49	$35.50	$35.50
Purchase #4	$19.44	7.204%	$20.8405	$20.84	$20.85	$20.80
Purchase #5	$97.52	4.458%	$101.8674	$101.87	$101.85	$101.90
Purchase #6	$93.77	11.456%	$104.5123	$104.51	$104.50	$104.50
Purchase #7	$64.37	5.452%	$67.8795	$67.88	$67.90	$67.90
7 purchase totals =	$603.52		$661.0030	$661.01	$661.00	$661.10