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	$34.48	6.872%	$36.8495	$36.85	$36.85	$36.80
Purchase #2	$202.27	10.390%	$223.2859	$223.29	$223.30	$223.30
Purchase #3	$127.26	3.317%	$131.4812	$131.48	$131.50	$131.50
Purchase #4	$42.51	9.150%	$46.3997	$46.40	$46.40	$46.40
Purchase #5	$68.78	3.605%	$71.2595	$71.26	$71.25	$71.30
Purchase #6	$190.28	3.309%	$196.5764	$196.58	$196.60	$196.60
Purchase #7	$214.51	6.756%	$229.0023	$229.00	$229.00	$229.00
7 purchase totals =	$880.09		$934.8545	$934.86	$934.90	$934.90