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	$128.98	3.810%	$133.8941	$133.89	$133.90	$133.90
Purchase #2	$79.59	9.837%	$87.4193	$87.42	$87.40	$87.40
Purchase #3	$39.47	3.523%	$40.8605	$40.86	$40.85	$40.90
Purchase #4	$158.69	12.232%	$178.101	$178.10	$178.10	$178.10
Purchase #5	$161.26	4.620%	$168.7102	$168.71	$168.70	$168.70
Purchase #6	$32.73	9.652%	$35.8891	$35.89	$35.90	$35.90
Purchase #7	$132.51	9.849%	$145.5609	$145.56	$145.55	$145.60
7 purchase totals =	$733.23		$790.4351	$790.43	$790.40	$790.50