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	$80.82	6.268%	$85.8858	$85.89	$85.90	$85.90
Purchase #2	$18.72	12.800%	$21.1162	$21.12	$21.10	$21.10
Purchase #3	$99.37	3.699%	$103.0457	$103.05	$103.05	$103.00
Purchase #4	$48.38	9.352%	$52.9045	$52.90	$52.90	$52.90
Purchase #5	$250.78	7.683%	$270.0474	$270.05	$270.05	$270.00
Purchase #6	$221.38	11.805%	$247.5139	$247.51	$247.50	$247.50
Purchase #7	$248.49	8.260%	$269.0153	$269.02	$269.00	$269.00
7 purchase totals =	$967.94		$1,049.5288	$1,049.54	$1,049.50	$1,049.40