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	$58.36	12.383%	$65.5867	$65.59	$65.60	$65.60
Purchase #2	$123.51	6.475%	$131.5073	$131.51	$131.50	$131.50
Purchase #3	$50.88	8.723%	$55.3183	$55.32	$55.30	$55.30
Purchase #4	$88.78	11.107%	$98.6408	$98.64	$98.65	$98.60
Purchase #5	$48.72	6.708%	$51.9881	$51.99	$52.00	$52.00
Purchase #6	$144.99	4.769%	$151.9046	$151.90	$151.90	$151.90
Purchase #7	$190.91	13.313%	$216.3258	$216.33	$216.35	$216.30
7 purchase totals =	$706.15		$771.2716	$771.28	$771.30	$771.20