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	$40.32	5.613%	$42.5832	$42.58	$42.60	$42.60
Purchase #2	$249.96	8.106%	$270.2218	$270.22	$270.20	$270.20
Purchase #3	$50.96	9.707%	$55.9067	$55.91	$55.90	$55.90
Purchase #4	$20.54	3.820%	$21.3246	$21.32	$21.30	$21.30
Purchase #5	$41.30	8.336%	$44.7428	$44.74	$44.75	$44.70
Purchase #6	$45.72	5.520%	$48.2437	$48.24	$48.25	$48.20
Purchase #7	$12.44	5.564%	$13.1322	$13.13	$13.15	$13.10
7 purchase totals =	$461.24		$496.1550	$496.14	$496.15	$496.00