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	$6.41	5.314%	$6.7506	$6.75	$6.75	$6.80
Purchase #2	$86.61	9.225%	$94.5998	$94.60	$94.60	$94.60
Purchase #3	$23.78	6.836%	$25.4056	$25.41	$25.40	$25.40
Purchase #4	$69.98	12.218%	$78.5302	$78.53	$78.55	$78.50
Purchase #5	$103.94	12.166%	$116.5853	$116.59	$116.60	$116.60
Purchase #6	$37.42	7.303%	$40.1528	$40.15	$40.15	$40.20
Purchase #7	$29.89	13.234%	$33.8456	$33.85	$33.85	$33.80
7 purchase totals =	$358.03		$395.8699	$395.88	$395.90	$395.90