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	$85.29	4.433%	$89.0709	$89.07	$89.05	$89.10
Purchase #2	$37.85	11.256%	$42.1104	$42.11	$42.10	$42.10
Purchase #3	$218.76	10.770%	$242.3205	$242.32	$242.30	$242.30
Purchase #4	$102.49	3.509%	$106.0864	$106.09	$106.10	$106.10
Purchase #5	$97.93	11.492%	$109.1841	$109.18	$109.20	$109.20
Purchase #6	$79.82	13.494%	$90.5909	$90.59	$90.60	$90.60
Purchase #7	$105.43	7.780%	$113.6325	$113.63	$113.65	$113.60
7 purchase totals =	$727.57		$792.9957	$792.99	$793.00	$793.00