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	$123.87	3.207%	$127.8425	$127.84	$127.85	$127.80
Purchase #2	$81.47	11.627%	$90.9425	$90.94	$90.95	$90.90
Purchase #3	$36.59	10.189%	$40.3182	$40.32	$40.30	$40.30
Purchase #4	$128.39	8.152%	$138.8564	$138.86	$138.85	$138.90
Purchase #5	$207.27	5.761%	$219.2108	$219.21	$219.20	$219.20
Purchase #6	$104.98	10.858%	$116.3787	$116.38	$116.40	$116.40
Purchase #7	$72.60	9.282%	$79.3387	$79.34	$79.35	$79.30
7 purchase totals =	$755.17		$812.8878	$812.89	$812.90	$812.80