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	$76.90	8.422%	$83.3765	$83.38	$83.40	$83.40
Purchase #2	$225.94	10.233%	$249.0604	$249.06	$249.05	$249.10
Purchase #3	$197.68	6.847%	$211.2151	$211.22	$211.20	$211.20
Purchase #4	$222.61	12.670%	$250.8147	$250.81	$250.80	$250.80
Purchase #5	$90.93	12.580%	$102.369	$102.37	$102.35	$102.40
Purchase #6	$18.38	8.266%	$19.8993	$19.90	$19.90	$19.90
Purchase #7	$190.78	12.479%	$214.5874	$214.59	$214.60	$214.60
7 purchase totals =	$1,023.22		$1,131.3224	$1,131.33	$1,131.30	$1,131.40