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	$76.90	8.793%	$83.6618	$83.66	$83.65	$83.70
Purchase #2	$137.51	4.401%	$143.5618	$143.56	$143.55	$143.60
Purchase #3	$24.44	4.740%	$25.5985	$25.60	$25.60	$25.60
Purchase #4	$97.55	11.772%	$109.0336	$109.03	$109.05	$109.00
Purchase #5	$85.38	4.758%	$89.4424	$89.44	$89.45	$89.40
Purchase #6	$85.95	4.383%	$89.7172	$89.72	$89.70	$89.70
Purchase #7	$192.73	11.248%	$214.4083	$214.41	$214.40	$214.40
7 purchase totals =	$700.46		$755.4236	$755.42	$755.40	$755.40