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	$55.36	9.319%	$60.519	$60.52	$60.50	$60.50
Purchase #2	$80.94	6.172%	$85.9356	$85.94	$85.95	$85.90
Purchase #3	$89.42	12.221%	$100.348	$100.35	$100.35	$100.30
Purchase #4	$27.37	6.490%	$29.1463	$29.15	$29.15	$29.10
Purchase #5	$23.47	6.690%	$25.0401	$25.04	$25.05	$25.00
Purchase #6	$206.90	13.267%	$234.3494	$234.35	$234.35	$234.30
Purchase #7	$53.99	10.573%	$59.6984	$59.70	$59.70	$59.70
7 purchase totals =	$537.45		$595.0368	$595.05	$595.05	$594.80