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	$37.52	12.419%	$42.1796	$42.18	$42.20	$42.20
Purchase #2	$150.40	4.303%	$156.8717	$156.87	$156.85	$156.90
Purchase #3	$96.81	7.426%	$103.9991	$104.00	$104.00	$104.00
Purchase #4	$181.52	13.346%	$205.7457	$205.75	$205.75	$205.70
Purchase #5	$52.79	5.193%	$55.5314	$55.53	$55.55	$55.50
Purchase #6	$196.90	7.582%	$211.829	$211.83	$211.85	$211.80
Purchase #7	$214.76	5.127%	$225.7707	$225.77	$225.75	$225.80
7 purchase totals =	$930.70		$1,001.9272	$1,001.93	$1,001.95	$1,001.90