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	$15.47	9.301%	$16.9089	$16.91	$16.90	$16.90
Purchase #2	$228.62	7.214%	$245.1126	$245.11	$245.10	$245.10
Purchase #3	$213.75	11.708%	$238.7759	$238.78	$238.80	$238.80
Purchase #4	$187.73	9.443%	$205.4573	$205.46	$205.45	$205.50
Purchase #5	$94.65	9.336%	$103.4865	$103.49	$103.50	$103.50
Purchase #6	$67.68	5.807%	$71.6102	$71.61	$71.60	$71.60
Purchase #7	$174.60	13.139%	$197.5407	$197.54	$197.55	$197.50
7 purchase totals =	$982.50		$1,078.8921	$1,078.90	$1,078.90	$1,078.90