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	$138.78	7.289%	$148.8957	$148.90	$148.90	$148.90
Purchase #2	$196.36	4.339%	$204.8801	$204.88	$204.90	$204.90
Purchase #3	$68.72	13.755%	$78.1724	$78.17	$78.15	$78.20
Purchase #4	$213.54	4.307%	$222.7372	$222.74	$222.75	$222.70
Purchase #5	$11.27	6.111%	$11.9587	$11.96	$11.95	$12.00
Purchase #6	$109.35	4.813%	$114.613	$114.61	$114.60	$114.60
Purchase #7	$129.78	6.233%	$137.8692	$137.87	$137.85	$137.90
7 purchase totals =	$867.80		$919.1263	$919.13	$919.10	$919.20