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	$109.89	10.493%	$121.4208	$121.42	$121.40	$121.40
Purchase #2	$116.71	12.413%	$131.1972	$131.20	$131.20	$131.20
Purchase #3	$142.43	6.177%	$151.2279	$151.23	$151.25	$151.20
Purchase #4	$93.50	13.112%	$105.7597	$105.76	$105.75	$105.80
Purchase #5	$162.47	9.813%	$178.4132	$178.41	$178.40	$178.40
Purchase #6	$99.99	9.492%	$109.4811	$109.48	$109.50	$109.50
Purchase #7	$79.51	7.227%	$85.2562	$85.26	$85.25	$85.30
7 purchase totals =	$804.50		$882.7561	$882.76	$882.75	$882.80