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	$80.80	12.336%	$90.7675	$90.77	$90.75	$90.80
Purchase #2	$106.59	9.207%	$116.4037	$116.40	$116.40	$116.40
Purchase #3	$123.40	11.562%	$137.6675	$137.67	$137.65	$137.70
Purchase #4	$231.77	5.436%	$244.369	$244.37	$244.35	$244.40
Purchase #5	$192.80	10.299%	$212.6565	$212.66	$212.65	$212.70
Purchase #6	$186.35	13.572%	$211.6414	$211.64	$211.65	$211.60
Purchase #7	$59.86	12.193%	$67.1587	$67.16	$67.15	$67.20
7 purchase totals =	$981.57		$1,080.6643	$1,080.67	$1,080.60	$1,080.80