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	$50.76	11.488%	$56.5913	$56.59	$56.60	$56.60
Purchase #2	$234.74	11.841%	$262.5356	$262.54	$262.55	$262.50
Purchase #3	$118.37	8.651%	$128.6102	$128.61	$128.60	$128.60
Purchase #4	$41.41	6.307%	$44.0217	$44.02	$44.00	$44.00
Purchase #5	$15.70	13.790%	$17.865	$17.87	$17.85	$17.90
Purchase #6	$35.42	4.827%	$37.1297	$37.13	$37.15	$37.10
Purchase #7	$6.53	13.345%	$7.4014	$7.40	$7.40	$7.40
7 purchase totals =	$502.93		$554.1549	$554.16	$554.15	$554.10