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	$159.83	5.616%	$168.8061	$168.81	$168.80	$168.80
Purchase #2	$118.27	11.330%	$131.67	$131.67	$131.65	$131.70
Purchase #3	$54.53	11.661%	$60.8887	$60.89	$60.90	$60.90
Purchase #4	$164.75	11.789%	$184.1724	$184.17	$184.15	$184.20
Purchase #5	$100.33	11.404%	$111.7716	$111.77	$111.75	$111.80
Purchase #6	$69.33	10.506%	$76.6138	$76.61	$76.60	$76.60
Purchase #7	$247.56	13.738%	$281.5698	$281.57	$281.55	$281.60
7 purchase totals =	$914.60		$1,015.4924	$1,015.49	$1,015.40	$1,015.60