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	$151.37	8.686%	$164.518	$164.52	$164.50	$164.50
Purchase #2	$26.63	10.869%	$29.5244	$29.52	$29.50	$29.50
Purchase #3	$31.41	5.620%	$33.1752	$33.18	$33.20	$33.20
Purchase #4	$64.27	3.244%	$66.3549	$66.35	$66.35	$66.40
Purchase #5	$125.41	5.706%	$132.5659	$132.57	$132.55	$132.60
Purchase #6	$30.63	8.806%	$33.3273	$33.33	$33.35	$33.30
Purchase #7	$37.74	4.598%	$39.4753	$39.48	$39.50	$39.50
7 purchase totals =	$467.46		$498.9410	$498.95	$498.95	$499.00