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	$178.27	4.263%	$185.8697	$185.87	$185.85	$185.90
Purchase #2	$211.72	10.756%	$234.4926	$234.49	$234.50	$234.50
Purchase #3	$142.49	5.349%	$150.1118	$150.11	$150.10	$150.10
Purchase #4	$164.77	8.527%	$178.8199	$178.82	$178.80	$178.80
Purchase #5	$25.63	3.436%	$26.5106	$26.51	$26.50	$26.50
Purchase #6	$37.84	9.433%	$41.4094	$41.41	$41.40	$41.40
Purchase #7	$88.40	13.816%	$100.6133	$100.61	$100.60	$100.60
7 purchase totals =	$849.12		$917.8273	$917.82	$917.75	$917.80