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	$50.85	11.747%	$56.8233	$56.82	$56.80	$56.80
Purchase #2	$34.35	3.276%	$35.4753	$35.48	$35.50	$35.50
Purchase #3	$9.59	4.427%	$10.0145	$10.01	$10.00	$10.00
Purchase #4	$50.37	7.837%	$54.3175	$54.32	$54.30	$54.30
Purchase #5	$108.88	7.339%	$116.8707	$116.87	$116.85	$116.90
Purchase #6	$160.77	4.600%	$168.1654	$168.17	$168.15	$168.20
Purchase #7	$220.49	12.404%	$247.8396	$247.84	$247.85	$247.80
7 purchase totals =	$635.30		$689.5063	$689.51	$689.45	$689.50