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	$221.75	5.496%	$233.9374	$233.94	$233.95	$233.90
Purchase #2	$129.89	12.300%	$145.8665	$145.87	$145.85	$145.90
Purchase #3	$199.42	6.300%	$211.9835	$211.98	$212.00	$212.00
Purchase #4	$90.81	8.218%	$98.2728	$98.27	$98.25	$98.30
Purchase #5	$66.62	6.752%	$71.1182	$71.12	$71.10	$71.10
Purchase #6	$99.35	9.855%	$109.1409	$109.14	$109.15	$109.10
Purchase #7	$109.26	3.861%	$113.4785	$113.48	$113.50	$113.50
7 purchase totals =	$917.10		$983.7978	$983.80	$983.80	$983.80