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	$62.90	7.213%	$67.437	$67.44	$67.45	$67.40
Purchase #2	$218.83	9.335%	$239.2578	$239.26	$239.25	$239.30
Purchase #3	$169.32	11.805%	$189.3082	$189.31	$189.30	$189.30
Purchase #4	$122.44	11.484%	$136.501	$136.50	$136.50	$136.50
Purchase #5	$206.26	5.787%	$218.1963	$218.20	$218.20	$218.20
Purchase #6	$63.60	4.131%	$66.2273	$66.23	$66.25	$66.20
Purchase #7	$247.83	12.701%	$279.3069	$279.31	$279.30	$279.30
7 purchase totals =	$1,091.18		$1,196.2345	$1,196.25	$1,196.25	$1,196.20