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	$6.96	6.391%	$7.4048	$7.40	$7.40	$7.40
Purchase #2	$121.37	9.199%	$132.5348	$132.53	$132.55	$132.50
Purchase #3	$42.60	10.566%	$47.1011	$47.10	$47.10	$47.10
Purchase #4	$36.66	3.440%	$37.9211	$37.92	$37.90	$37.90
Purchase #5	$68.75	5.525%	$72.5484	$72.55	$72.55	$72.50
Purchase #6	$200.63	7.414%	$215.5047	$215.50	$215.50	$215.50
Purchase #7	$159.65	5.732%	$168.8011	$168.80	$168.80	$168.80
7 purchase totals =	$636.62		$681.8160	$681.80	$681.80	$681.70