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	$80.54	9.580%	$88.2557	$88.26	$88.25	$88.30
Purchase #2	$180.31	4.457%	$188.3464	$188.35	$188.35	$188.30
Purchase #3	$88.30	9.410%	$96.609	$96.61	$96.60	$96.60
Purchase #4	$227.34	5.519%	$239.8869	$239.89	$239.90	$239.90
Purchase #5	$143.76	12.622%	$161.9054	$161.91	$161.90	$161.90
Purchase #6	$160.41	12.606%	$180.6313	$180.63	$180.65	$180.60
Purchase #7	$133.50	8.184%	$144.4256	$144.43	$144.45	$144.40
7 purchase totals =	$1,014.16		$1,100.0603	$1,100.08	$1,100.10	$1,100.00