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	$158.29	6.704%	$168.9018	$168.90	$168.90	$168.90
Purchase #2	$193.74	4.213%	$201.9023	$201.90	$201.90	$201.90
Purchase #3	$89.44	3.411%	$92.4908	$92.49	$92.50	$92.50
Purchase #4	$118.83	7.674%	$127.949	$127.95	$127.95	$127.90
Purchase #5	$72.69	9.361%	$79.4945	$79.49	$79.50	$79.50
Purchase #6	$44.41	3.217%	$45.8387	$45.84	$45.85	$45.80
Purchase #7	$196.73	13.371%	$223.0348	$223.03	$223.05	$223.00
7 purchase totals =	$874.13		$939.6119	$939.60	$939.65	$939.50