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	$99.65	13.395%	$112.9981	$113.00	$113.00	$113.00
Purchase #2	$165.97	11.322%	$184.7611	$184.76	$184.75	$184.80
Purchase #3	$29.41	11.105%	$32.676	$32.68	$32.70	$32.70
Purchase #4	$87.33	3.749%	$90.604	$90.60	$90.60	$90.60
Purchase #5	$127.26	3.167%	$131.2903	$131.29	$131.30	$131.30
Purchase #6	$5.60	5.762%	$5.9227	$5.92	$5.90	$5.90
Purchase #7	$105.52	6.498%	$112.3767	$112.38	$112.40	$112.40
7 purchase totals =	$620.74		$670.6289	$670.63	$670.65	$670.70