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	$227.78	9.374%	$249.1321	$249.13	$249.15	$249.10
Purchase #2	$182.60	9.703%	$200.3177	$200.32	$200.30	$200.30
Purchase #3	$138.63	6.554%	$147.7158	$147.72	$147.70	$147.70
Purchase #4	$65.49	10.734%	$72.5197	$72.52	$72.50	$72.50
Purchase #5	$223.37	13.811%	$254.2196	$254.22	$254.20	$254.20
Purchase #6	$16.43	13.230%	$18.6037	$18.60	$18.60	$18.60
Purchase #7	$165.97	12.173%	$186.1735	$186.17	$186.15	$186.20
7 purchase totals =	$1,020.27		$1,128.6821	$1,128.68	$1,128.60	$1,128.60