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	$62.37	6.799%	$66.6105	$66.61	$66.60	$66.60
Purchase #2	$246.60	13.398%	$279.6395	$279.64	$279.65	$279.60
Purchase #3	$59.30	12.495%	$66.7095	$66.71	$66.70	$66.70
Purchase #4	$7.30	4.297%	$7.6137	$7.61	$7.60	$7.60
Purchase #5	$194.43	10.747%	$215.3254	$215.33	$215.35	$215.30
Purchase #6	$55.34	6.109%	$58.7207	$58.72	$58.70	$58.70
Purchase #7	$164.42	12.589%	$185.1188	$185.12	$185.10	$185.10
7 purchase totals =	$789.76		$879.7381	$879.74	$879.70	$879.60