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	$33.98	4.115%	$35.3783	$35.38	$35.40	$35.40
Purchase #2	$126.60	3.733%	$131.326	$131.33	$131.35	$131.30
Purchase #3	$92.98	13.859%	$105.8661	$105.87	$105.85	$105.90
Purchase #4	$17.86	3.645%	$18.511	$18.51	$18.50	$18.50
Purchase #5	$54.66	9.204%	$59.6909	$59.69	$59.70	$59.70
Purchase #6	$30.46	7.362%	$32.7025	$32.70	$32.70	$32.70
Purchase #7	$14.83	6.440%	$15.7851	$15.79	$15.80	$15.80
7 purchase totals =	$371.37		$399.2599	$399.27	$399.30	$399.30