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	$241.85	12.432%	$271.9168	$271.92	$271.90	$271.90
Purchase #2	$53.48	13.750%	$60.8335	$60.83	$60.85	$60.80
Purchase #3	$40.52	12.189%	$45.459	$45.46	$45.45	$45.50
Purchase #4	$29.69	4.839%	$31.1267	$31.13	$31.15	$31.10
Purchase #5	$237.72	4.787%	$249.0997	$249.10	$249.10	$249.10
Purchase #6	$198.91	3.775%	$206.4189	$206.42	$206.40	$206.40
Purchase #7	$246.93	12.623%	$278.1	$278.10	$278.10	$278.10
7 purchase totals =	$1,049.10		$1,142.9546	$1,142.96	$1,142.95	$1,142.90