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	$246.54	7.842%	$265.8737	$265.87	$265.85	$265.90
Purchase #2	$139.70	11.603%	$155.9094	$155.91	$155.90	$155.90
Purchase #3	$8.51	6.825%	$9.0908	$9.09	$9.10	$9.10
Purchase #4	$9.98	4.765%	$10.4555	$10.46	$10.45	$10.50
Purchase #5	$138.85	10.115%	$152.8947	$152.89	$152.90	$152.90
Purchase #6	$10.46	11.623%	$11.6758	$11.68	$11.70	$11.70
Purchase #7	$99.89	5.471%	$105.355	$105.36	$105.35	$105.40
7 purchase totals =	$653.93		$711.2549	$711.26	$711.25	$711.40