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	$127.77	9.430%	$139.8187	$139.82	$139.80	$139.80
Purchase #2	$207.38	13.212%	$234.779	$234.78	$234.80	$234.80
Purchase #3	$229.79	7.474%	$246.9645	$246.96	$246.95	$247.00
Purchase #4	$42.31	8.344%	$45.8403	$45.84	$45.85	$45.80
Purchase #5	$92.66	13.805%	$105.4517	$105.45	$105.45	$105.50
Purchase #6	$17.29	11.567%	$19.2899	$19.29	$19.30	$19.30
Purchase #7	$192.32	11.108%	$213.6829	$213.68	$213.70	$213.70
7 purchase totals =	$909.52		$1,005.8270	$1,005.82	$1,005.85	$1,005.90