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	$227.52	9.273%	$248.6179	$248.62	$248.60	$248.60
Purchase #2	$90.25	5.732%	$95.4231	$95.42	$95.40	$95.40
Purchase #3	$24.62	8.573%	$26.7307	$26.73	$26.75	$26.70
Purchase #4	$84.75	11.778%	$94.7319	$94.73	$94.75	$94.70
Purchase #5	$151.48	13.496%	$171.9237	$171.92	$171.90	$171.90
Purchase #6	$51.64	5.671%	$54.5685	$54.57	$54.55	$54.60
Purchase #7	$96.84	3.793%	$100.5131	$100.51	$100.50	$100.50
7 purchase totals =	$727.10		$792.5089	$792.50	$792.45	$792.40