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	$86.39	6.665%	$92.1479	$92.15	$92.15	$92.10
Purchase #2	$249.57	13.277%	$282.7054	$282.71	$282.70	$282.70
Purchase #3	$15.54	11.744%	$17.365	$17.37	$17.35	$17.40
Purchase #4	$204.63	13.302%	$231.8499	$231.85	$231.85	$231.80
Purchase #5	$87.86	8.706%	$95.5091	$95.51	$95.50	$95.50
Purchase #6	$184.71	6.633%	$196.9618	$196.96	$196.95	$197.00
Purchase #7	$55.63	11.554%	$62.0575	$62.06	$62.05	$62.10
7 purchase totals =	$884.33		$978.5966	$978.61	$978.55	$978.60