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	$28.34	11.175%	$31.507	$31.51	$31.50	$31.50
Purchase #2	$233.54	7.307%	$250.6048	$250.60	$250.60	$250.60
Purchase #3	$207.70	4.636%	$217.329	$217.33	$217.35	$217.30
Purchase #4	$150.42	9.873%	$165.271	$165.27	$165.25	$165.30
Purchase #5	$40.97	13.420%	$46.4682	$46.47	$46.45	$46.50
Purchase #6	$101.90	9.376%	$111.4541	$111.45	$111.45	$111.50
Purchase #7	$168.40	10.872%	$186.7084	$186.71	$186.70	$186.70
7 purchase totals =	$931.27		$1,009.3425	$1,009.34	$1,009.30	$1,009.40