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	$38.68	7.591%	$41.6162	$41.62	$41.60	$41.60
Purchase #2	$157.96	5.402%	$166.493	$166.49	$166.50	$166.50
Purchase #3	$87.95	4.795%	$92.1672	$92.17	$92.15	$92.20
Purchase #4	$95.65	4.485%	$99.9399	$99.94	$99.95	$99.90
Purchase #5	$81.72	4.811%	$85.6515	$85.65	$85.65	$85.70
Purchase #6	$88.74	12.519%	$99.8494	$99.85	$99.85	$99.80
Purchase #7	$232.95	9.181%	$254.3371	$254.34	$254.35	$254.30
7 purchase totals =	$783.65		$840.0543	$840.06	$840.05	$840.00