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	$86.44	5.189%	$90.9254	$90.93	$90.95	$90.90
Purchase #2	$196.39	11.385%	$218.749	$218.75	$218.75	$218.70
Purchase #3	$70.68	12.574%	$79.5673	$79.57	$79.55	$79.60
Purchase #4	$211.35	6.594%	$225.2864	$225.29	$225.30	$225.30
Purchase #5	$50.71	11.472%	$56.5275	$56.53	$56.55	$56.50
Purchase #6	$61.49	12.124%	$68.945	$68.95	$68.95	$68.90
Purchase #7	$222.57	7.149%	$238.4815	$238.48	$238.50	$238.50
7 purchase totals =	$899.63		$978.4821	$978.50	$978.55	$978.40