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	$128.33	3.256%	$132.5084	$132.51	$132.50	$132.50
Purchase #2	$165.83	9.383%	$181.3898	$181.39	$181.40	$181.40
Purchase #3	$240.38	6.694%	$256.471	$256.47	$256.45	$256.50
Purchase #4	$109.58	9.586%	$120.0843	$120.08	$120.10	$120.10
Purchase #5	$33.65	6.259%	$35.7562	$35.76	$35.75	$35.80
Purchase #6	$49.53	13.110%	$56.0234	$56.02	$56.00	$56.00
Purchase #7	$111.48	13.477%	$126.5042	$126.50	$126.50	$126.50
7 purchase totals =	$838.78		$908.7373	$908.73	$908.70	$908.80