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	$51.57	10.279%	$56.8709	$56.87	$56.85	$56.90
Purchase #2	$41.76	6.510%	$44.4786	$44.48	$44.50	$44.50
Purchase #3	$42.25	13.361%	$47.895	$47.90	$47.90	$47.90
Purchase #4	$94.89	7.668%	$102.1662	$102.17	$102.15	$102.20
Purchase #5	$216.98	7.601%	$233.4726	$233.47	$233.45	$233.50
Purchase #6	$80.51	10.821%	$89.222	$89.22	$89.20	$89.20
Purchase #7	$186.61	10.657%	$206.497	$206.50	$206.50	$206.50
7 purchase totals =	$714.57		$780.6023	$780.61	$780.55	$780.70