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	$34.39	8.732%	$37.3929	$37.39	$37.40	$37.40
Purchase #2	$171.77	13.442%	$194.8593	$194.86	$194.85	$194.90
Purchase #3	$231.83	4.595%	$242.4826	$242.48	$242.50	$242.50
Purchase #4	$167.69	13.708%	$190.6769	$190.68	$190.70	$190.70
Purchase #5	$11.41	8.750%	$12.4084	$12.41	$12.40	$12.40
Purchase #6	$64.76	11.872%	$72.4483	$72.45	$72.45	$72.40
Purchase #7	$250.31	12.384%	$281.3084	$281.31	$281.30	$281.30
7 purchase totals =	$932.16		$1,031.5768	$1,031.58	$1,031.60	$1,031.60