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	$172.52	4.652%	$180.5456	$180.55	$180.55	$180.50
Purchase #2	$209.47	7.194%	$224.5393	$224.54	$224.55	$224.50
Purchase #3	$129.65	9.257%	$141.6517	$141.65	$141.65	$141.70
Purchase #4	$210.55	6.818%	$224.9053	$224.91	$224.90	$224.90
Purchase #5	$131.38	6.264%	$139.6096	$139.61	$139.60	$139.60
Purchase #6	$113.30	12.639%	$127.62	$127.62	$127.60	$127.60
Purchase #7	$25.87	5.609%	$27.321	$27.32	$27.30	$27.30
7 purchase totals =	$992.74		$1,066.1925	$1,066.20	$1,066.15	$1,066.10