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	$160.52	11.424%	$178.8578	$178.86	$178.85	$178.90
Purchase #2	$176.69	6.103%	$187.4734	$187.47	$187.45	$187.50
Purchase #3	$167.67	5.470%	$176.8415	$176.84	$176.85	$176.80
Purchase #4	$96.40	7.200%	$103.3408	$103.34	$103.35	$103.30
Purchase #5	$61.93	8.386%	$67.1234	$67.12	$67.10	$67.10
Purchase #6	$46.95	7.814%	$50.6187	$50.62	$50.60	$50.60
Purchase #7	$139.83	7.765%	$150.6878	$150.69	$150.70	$150.70
7 purchase totals =	$849.99		$914.9434	$914.94	$914.90	$914.90