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	$249.48	11.326%	$277.7361	$277.74	$277.75	$277.70
Purchase #2	$189.83	3.619%	$196.6999	$196.70	$196.70	$196.70
Purchase #3	$13.25	4.462%	$13.8412	$13.84	$13.85	$13.80
Purchase #4	$159.60	6.136%	$169.3931	$169.39	$169.40	$169.40
Purchase #5	$248.95	6.742%	$265.7342	$265.73	$265.75	$265.70
Purchase #6	$112.59	13.440%	$127.7221	$127.72	$127.70	$127.70
Purchase #7	$165.57	13.190%	$187.4087	$187.41	$187.40	$187.40
7 purchase totals =	$1,139.27		$1,238.5353	$1,238.53	$1,238.55	$1,238.40