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	$183.51	8.113%	$198.3982	$198.40	$198.40	$198.40
Purchase #2	$19.71	5.673%	$20.8281	$20.83	$20.85	$20.80
Purchase #3	$105.45	7.590%	$113.4537	$113.45	$113.45	$113.50
Purchase #4	$181.43	5.158%	$190.7882	$190.79	$190.80	$190.80
Purchase #5	$64.49	11.367%	$71.8206	$71.82	$71.80	$71.80
Purchase #6	$247.34	13.173%	$279.9221	$279.92	$279.90	$279.90
Purchase #7	$201.78	13.192%	$228.3988	$228.40	$228.40	$228.40
7 purchase totals =	$1,003.71		$1,103.6097	$1,103.61	$1,103.60	$1,103.60