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	$100.37	9.209%	$109.6131	$109.61	$109.60	$109.60
Purchase #2	$64.49	12.393%	$72.4822	$72.48	$72.50	$72.50
Purchase #3	$87.29	5.256%	$91.878	$91.88	$91.90	$91.90
Purchase #4	$226.28	7.576%	$243.423	$243.42	$243.40	$243.40
Purchase #5	$6.97	5.681%	$7.366	$7.37	$7.35	$7.40
Purchase #6	$118.27	7.463%	$127.0965	$127.10	$127.10	$127.10
Purchase #7	$134.31	6.804%	$143.4485	$143.45	$143.45	$143.40
7 purchase totals =	$737.98		$795.3073	$795.31	$795.30	$795.30