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	$186.47	13.641%	$211.9064	$211.91	$211.90	$211.90
Purchase #2	$79.34	13.289%	$89.8835	$89.88	$89.90	$89.90
Purchase #3	$141.78	12.141%	$158.9935	$158.99	$159.00	$159.00
Purchase #4	$145.76	13.284%	$165.1228	$165.12	$165.10	$165.10
Purchase #5	$10.99	9.573%	$12.0421	$12.04	$12.05	$12.00
Purchase #6	$77.67	5.638%	$82.049	$82.05	$82.05	$82.00
Purchase #7	$85.47	8.328%	$92.5879	$92.59	$92.60	$92.60
7 purchase totals =	$727.48		$812.5852	$812.58	$812.60	$812.50