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	$87.52	3.215%	$90.3338	$90.33	$90.35	$90.30
Purchase #2	$193.28	5.870%	$204.6255	$204.63	$204.65	$204.60
Purchase #3	$209.83	13.793%	$238.7719	$238.77	$238.75	$238.80
Purchase #4	$244.72	11.523%	$272.9191	$272.92	$272.90	$272.90
Purchase #5	$107.83	8.607%	$117.1109	$117.11	$117.10	$117.10
Purchase #6	$5.48	10.610%	$6.0614	$6.06	$6.05	$6.10
Purchase #7	$109.80	11.179%	$122.0745	$122.07	$122.05	$122.10
7 purchase totals =	$958.46		$1,051.8971	$1,051.89	$1,051.85	$1,051.90