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	$52.95	4.315%	$55.2348	$55.23	$55.25	$55.20
Purchase #2	$241.35	7.263%	$258.8793	$258.88	$258.90	$258.90
Purchase #3	$45.33	12.110%	$50.8195	$50.82	$50.80	$50.80
Purchase #4	$116.64	3.352%	$120.5498	$120.55	$120.55	$120.50
Purchase #5	$10.92	8.316%	$11.8281	$11.83	$11.85	$11.80
Purchase #6	$86.96	13.268%	$98.4979	$98.50	$98.50	$98.50
Purchase #7	$29.57	5.647%	$31.2398	$31.24	$31.25	$31.20
7 purchase totals =	$583.72		$627.0492	$627.05	$627.10	$626.90