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	$54.42	9.349%	$59.5077	$59.51	$59.50	$59.50
Purchase #2	$142.29	11.216%	$158.2492	$158.25	$158.25	$158.20
Purchase #3	$92.52	12.674%	$104.246	$104.25	$104.25	$104.20
Purchase #4	$226.99	8.151%	$245.492	$245.49	$245.50	$245.50
Purchase #5	$15.92	11.323%	$17.7226	$17.72	$17.70	$17.70
Purchase #6	$187.40	4.186%	$195.2446	$195.24	$195.25	$195.20
Purchase #7	$39.34	11.390%	$43.8208	$43.82	$43.80	$43.80
7 purchase totals =	$758.88		$824.2829	$824.28	$824.25	$824.10