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	$30.73	3.407%	$31.777	$31.78	$31.80	$31.80
Purchase #2	$123.89	6.108%	$131.4572	$131.46	$131.45	$131.50
Purchase #3	$175.33	7.832%	$189.0618	$189.06	$189.05	$189.10
Purchase #4	$37.76	9.153%	$41.2162	$41.22	$41.20	$41.20
Purchase #5	$76.72	8.389%	$83.156	$83.16	$83.15	$83.20
Purchase #6	$8.97	13.544%	$10.1849	$10.18	$10.20	$10.20
Purchase #7	$79.55	4.605%	$83.2133	$83.21	$83.20	$83.20
7 purchase totals =	$532.95		$570.0664	$570.07	$570.05	$570.20