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	$147.76	13.837%	$168.2056	$168.21	$168.20	$168.20
Purchase #2	$220.63	13.725%	$250.9115	$250.91	$250.90	$250.90
Purchase #3	$127.53	10.832%	$141.344	$141.34	$141.35	$141.30
Purchase #4	$61.91	7.242%	$66.3935	$66.39	$66.40	$66.40
Purchase #5	$216.45	4.641%	$226.4954	$226.50	$226.50	$226.50
Purchase #6	$56.38	5.652%	$59.5666	$59.57	$59.55	$59.60
Purchase #7	$79.93	12.592%	$89.9948	$89.99	$90.00	$90.00
7 purchase totals =	$910.59		$1,002.9114	$1,002.91	$1,002.90	$1,002.90