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	$37.37	9.147%	$40.7882	$40.79	$40.80	$40.80
Purchase #2	$146.30	11.802%	$163.5663	$163.57	$163.55	$163.60
Purchase #3	$111.46	11.807%	$124.6201	$124.62	$124.60	$124.60
Purchase #4	$67.61	10.352%	$74.609	$74.61	$74.60	$74.60
Purchase #5	$137.94	10.420%	$152.3133	$152.31	$152.30	$152.30
Purchase #6	$219.94	7.747%	$236.9788	$236.98	$237.00	$237.00
Purchase #7	$186.69	5.238%	$196.4688	$196.47	$196.45	$196.50
7 purchase totals =	$907.31		$989.3445	$989.35	$989.30	$989.40