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	$16.67	7.591%	$17.9354	$17.94	$17.95	$17.90
Purchase #2	$232.45	4.235%	$242.2943	$242.29	$242.30	$242.30
Purchase #3	$142.64	9.650%	$156.4048	$156.40	$156.40	$156.40
Purchase #4	$61.83	8.800%	$67.271	$67.27	$67.25	$67.30
Purchase #5	$239.59	3.572%	$248.1482	$248.15	$248.15	$248.10
Purchase #6	$99.81	9.240%	$109.0324	$109.03	$109.05	$109.00
Purchase #7	$219.47	11.572%	$244.8671	$244.87	$244.85	$244.90
7 purchase totals =	$1,012.46		$1,085.9532	$1,085.95	$1,085.95	$1,085.90