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	$180.63	5.105%	$189.8512	$189.85	$189.85	$189.90
Purchase #2	$167.64	7.357%	$179.9733	$179.97	$179.95	$180.00
Purchase #3	$41.27	12.335%	$46.3607	$46.36	$46.35	$46.40
Purchase #4	$116.38	10.419%	$128.5056	$128.51	$128.50	$128.50
Purchase #5	$9.29	9.792%	$10.1997	$10.20	$10.20	$10.20
Purchase #6	$78.80	9.586%	$86.3538	$86.35	$86.35	$86.40
Purchase #7	$172.88	7.336%	$185.5625	$185.56	$185.55	$185.60
7 purchase totals =	$766.89		$826.8068	$826.80	$826.75	$827.00