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	$103.53	6.130%	$109.8764	$109.88	$109.90	$109.90
Purchase #2	$48.29	5.507%	$50.9493	$50.95	$50.95	$50.90
Purchase #3	$248.90	9.226%	$271.8635	$271.86	$271.85	$271.90
Purchase #4	$241.78	5.434%	$254.9183	$254.92	$254.90	$254.90
Purchase #5	$52.51	3.304%	$54.2449	$54.24	$54.25	$54.20
Purchase #6	$9.30	4.464%	$9.7152	$9.72	$9.70	$9.70
Purchase #7	$56.82	4.557%	$59.4093	$59.41	$59.40	$59.40
7 purchase totals =	$761.13		$810.9769	$810.98	$810.95	$810.90