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	$25.41	11.417%	$28.3111	$28.31	$28.30	$28.30
Purchase #2	$127.63	6.151%	$135.4805	$135.48	$135.50	$135.50
Purchase #3	$198.84	13.238%	$225.1624	$225.16	$225.15	$225.20
Purchase #4	$12.95	4.262%	$13.5019	$13.50	$13.50	$13.50
Purchase #5	$66.32	9.332%	$72.509	$72.51	$72.50	$72.50
Purchase #6	$250.62	10.290%	$276.4088	$276.41	$276.40	$276.40
Purchase #7	$109.46	8.240%	$118.4795	$118.48	$118.50	$118.50
7 purchase totals =	$791.23		$869.8532	$869.85	$869.85	$869.90