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	$88.46	3.420%	$91.4853	$91.49	$91.50	$91.50
Purchase #2	$52.99	11.430%	$59.0468	$59.05	$59.05	$59.00
Purchase #3	$87.39	3.594%	$90.5308	$90.53	$90.55	$90.50
Purchase #4	$124.76	13.246%	$141.2857	$141.29	$141.30	$141.30
Purchase #5	$89.92	8.715%	$97.7565	$97.76	$97.75	$97.80
Purchase #6	$120.46	6.418%	$128.1911	$128.19	$128.20	$128.20
Purchase #7	$130.50	7.726%	$140.5824	$140.58	$140.60	$140.60
7 purchase totals =	$694.48		$748.8786	$748.89	$748.95	$748.90