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	$28.89	12.692%	$32.5567	$32.56	$32.55	$32.60
Purchase #2	$145.47	9.722%	$159.6126	$159.61	$159.60	$159.60
Purchase #3	$186.78	13.736%	$212.4361	$212.44	$212.45	$212.40
Purchase #4	$229.87	10.308%	$253.565	$253.57	$253.55	$253.60
Purchase #5	$204.46	6.656%	$218.0689	$218.07	$218.05	$218.10
Purchase #6	$121.96	4.176%	$127.053	$127.05	$127.05	$127.10
Purchase #7	$243.90	7.466%	$262.1096	$262.11	$262.10	$262.10
7 purchase totals =	$1,161.33		$1,265.4019	$1,265.41	$1,265.35	$1,265.50