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	$236.54	5.187%	$248.8093	$248.81	$248.80	$248.80
Purchase #2	$160.44	7.223%	$172.0286	$172.03	$172.05	$172.00
Purchase #3	$96.94	3.715%	$100.5413	$100.54	$100.55	$100.50
Purchase #4	$194.34	10.605%	$214.9498	$214.95	$214.95	$214.90
Purchase #5	$93.42	5.753%	$98.7945	$98.79	$98.80	$98.80
Purchase #6	$35.40	12.190%	$39.7153	$39.72	$39.70	$39.70
Purchase #7	$223.25	8.321%	$241.8266	$241.83	$241.85	$241.80
7 purchase totals =	$1,040.33		$1,116.6654	$1,116.67	$1,116.70	$1,116.50