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	$50.34	9.651%	$55.1983	$55.20	$55.20	$55.20
Purchase #2	$52.50	6.852%	$56.0973	$56.10	$56.10	$56.10
Purchase #3	$47.69	8.650%	$51.8152	$51.82	$51.80	$51.80
Purchase #4	$96.33	13.842%	$109.664	$109.66	$109.65	$109.70
Purchase #5	$79.99	12.697%	$90.1463	$90.15	$90.15	$90.10
Purchase #6	$38.54	4.228%	$40.1695	$40.17	$40.15	$40.20
Purchase #7	$126.27	6.183%	$134.0773	$134.08	$134.10	$134.10
7 purchase totals =	$491.66		$537.1679	$537.18	$537.15	$537.20