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	$89.32	10.403%	$98.612	$98.61	$98.60	$98.60
Purchase #2	$119.32	3.487%	$123.4807	$123.48	$123.50	$123.50
Purchase #3	$92.91	9.368%	$101.6138	$101.61	$101.60	$101.60
Purchase #4	$132.26	7.854%	$142.6477	$142.65	$142.65	$142.60
Purchase #5	$32.37	12.431%	$36.3939	$36.39	$36.40	$36.40
Purchase #6	$114.47	11.680%	$127.8401	$127.84	$127.85	$127.80
Purchase #7	$174.54	3.123%	$179.9909	$179.99	$180.00	$180.00
7 purchase totals =	$755.19		$810.5791	$810.57	$810.60	$810.50