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	$33.34	11.591%	$37.2044	$37.20	$37.20	$37.20
Purchase #2	$181.53	7.743%	$195.5859	$195.59	$195.60	$195.60
Purchase #3	$217.86	6.145%	$231.2475	$231.25	$231.25	$231.20
Purchase #4	$89.36	6.639%	$95.2926	$95.29	$95.30	$95.30
Purchase #5	$127.34	11.447%	$141.9166	$141.92	$141.90	$141.90
Purchase #6	$102.63	6.235%	$109.029	$109.03	$109.05	$109.00
Purchase #7	$9.37	11.250%	$10.4241	$10.42	$10.40	$10.40
7 purchase totals =	$761.43		$820.7001	$820.70	$820.70	$820.60