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	$238.85	7.835%	$257.5639	$257.56	$257.55	$257.60
Purchase #2	$80.89	5.605%	$85.4239	$85.42	$85.40	$85.40
Purchase #3	$71.82	13.814%	$81.7412	$81.74	$81.75	$81.70
Purchase #4	$39.44	11.405%	$43.9381	$43.94	$43.95	$43.90
Purchase #5	$41.92	8.566%	$45.5109	$45.51	$45.50	$45.50
Purchase #6	$12.46	3.241%	$12.8638	$12.86	$12.85	$12.90
Purchase #7	$108.59	7.128%	$116.3303	$116.33	$116.35	$116.30
7 purchase totals =	$593.97		$643.3721	$643.36	$643.35	$643.30