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	$15.57	4.752%	$16.3099	$16.31	$16.30	$16.30
Purchase #2	$42.79	6.394%	$45.526	$45.53	$45.55	$45.50
Purchase #3	$40.46	7.137%	$43.3476	$43.35	$43.35	$43.30
Purchase #4	$11.47	5.179%	$12.064	$12.06	$12.05	$12.10
Purchase #5	$45.88	13.557%	$52.1	$52.10	$52.10	$52.10
Purchase #6	$28.33	12.570%	$31.8911	$31.89	$31.90	$31.90
Purchase #7	$138.83	3.598%	$143.8251	$143.83	$143.85	$143.80
7 purchase totals =	$323.33		$345.0637	$345.07	$345.10	$345.00