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	$107.36	10.191%	$118.3011	$118.30	$118.30	$118.30
Purchase #2	$24.85	10.457%	$27.4486	$27.45	$27.45	$27.40
Purchase #3	$15.26	10.727%	$16.8969	$16.90	$16.90	$16.90
Purchase #4	$52.90	12.365%	$59.4411	$59.44	$59.45	$59.40
Purchase #5	$220.35	10.781%	$244.1059	$244.11	$244.10	$244.10
Purchase #6	$61.46	9.491%	$67.2932	$67.29	$67.30	$67.30
Purchase #7	$21.27	7.600%	$22.8865	$22.89	$22.90	$22.90
7 purchase totals =	$503.45		$556.3733	$556.38	$556.40	$556.30