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	$241.51	10.266%	$266.3034	$266.30	$266.30	$266.30
Purchase #2	$78.43	12.798%	$88.4675	$88.47	$88.45	$88.50
Purchase #3	$64.78	4.132%	$67.4567	$67.46	$67.45	$67.50
Purchase #4	$189.94	3.220%	$196.0561	$196.06	$196.05	$196.10
Purchase #5	$31.66	13.294%	$35.8689	$35.87	$35.85	$35.90
Purchase #6	$214.51	13.551%	$243.5783	$243.58	$243.60	$243.60
Purchase #7	$239.87	4.815%	$251.4197	$251.42	$251.40	$251.40
7 purchase totals =	$1,060.70		$1,149.1506	$1,149.16	$1,149.10	$1,149.30