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	$7.49	5.502%	$7.9021	$7.90	$7.90	$7.90
Purchase #2	$104.36	7.451%	$112.1359	$112.14	$112.15	$112.10
Purchase #3	$172.95	13.832%	$196.8724	$196.87	$196.85	$196.90
Purchase #4	$23.88	7.132%	$25.5831	$25.58	$25.60	$25.60
Purchase #5	$81.79	9.200%	$89.3147	$89.31	$89.30	$89.30
Purchase #6	$136.68	10.735%	$151.3526	$151.35	$151.35	$151.40
Purchase #7	$39.50	13.458%	$44.8159	$44.82	$44.80	$44.80
7 purchase totals =	$566.65		$627.9767	$627.97	$627.95	$628.00