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	$168.47	12.821%	$190.0695	$190.07	$190.05	$190.10
Purchase #2	$88.51	10.161%	$97.5035	$97.50	$97.50	$97.50
Purchase #3	$224.65	3.240%	$231.9287	$231.93	$231.95	$231.90
Purchase #4	$105.88	3.454%	$109.5371	$109.54	$109.55	$109.50
Purchase #5	$127.59	6.856%	$136.3376	$136.34	$136.35	$136.30
Purchase #6	$29.41	4.144%	$30.6288	$30.63	$30.65	$30.60
Purchase #7	$169.56	6.172%	$180.0252	$180.03	$180.05	$180.00
7 purchase totals =	$914.07		$976.0304	$976.04	$976.10	$975.90