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	$17.46	9.580%	$19.1327	$19.13	$19.15	$19.10
Purchase #2	$8.77	12.744%	$9.8876	$9.89	$9.90	$9.90
Purchase #3	$82.57	9.788%	$90.652	$90.65	$90.65	$90.70
Purchase #4	$132.45	13.832%	$150.7705	$150.77	$150.75	$150.80
Purchase #5	$32.36	10.742%	$35.8361	$35.84	$35.85	$35.80
Purchase #6	$159.60	5.635%	$168.5935	$168.59	$168.60	$168.60
Purchase #7	$179.95	10.390%	$198.6468	$198.65	$198.65	$198.60
7 purchase totals =	$613.16		$673.5192	$673.52	$673.55	$673.50