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	$126.63	10.181%	$139.5222	$139.52	$139.50	$139.50
Purchase #2	$101.80	5.462%	$107.3603	$107.36	$107.35	$107.40
Purchase #3	$91.48	11.302%	$101.8191	$101.82	$101.80	$101.80
Purchase #4	$48.31	13.206%	$54.6898	$54.69	$54.70	$54.70
Purchase #5	$151.64	13.860%	$172.6573	$172.66	$172.65	$172.70
Purchase #6	$209.91	6.486%	$223.5248	$223.52	$223.50	$223.50
Purchase #7	$35.81	4.788%	$37.5246	$37.52	$37.50	$37.50
7 purchase totals =	$765.58		$837.0981	$837.09	$837.00	$837.10