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	$249.39	7.779%	$268.79	$268.79	$268.80	$268.80
Purchase #2	$118.30	7.792%	$127.5179	$127.52	$127.50	$127.50
Purchase #3	$104.96	12.592%	$118.1766	$118.18	$118.20	$118.20
Purchase #4	$219.71	12.858%	$247.9603	$247.96	$247.95	$248.00
Purchase #5	$64.69	12.228%	$72.6003	$72.60	$72.60	$72.60
Purchase #6	$169.77	9.141%	$185.2887	$185.29	$185.30	$185.30
Purchase #7	$184.48	7.303%	$197.9526	$197.95	$197.95	$198.00
7 purchase totals =	$1,111.30		$1,218.2864	$1,218.29	$1,218.30	$1,218.40