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	$43.28	8.297%	$46.8709	$46.87	$46.85	$46.90
Purchase #2	$152.62	6.107%	$161.9405	$161.94	$161.95	$161.90
Purchase #3	$229.77	12.381%	$258.2178	$258.22	$258.20	$258.20
Purchase #4	$219.30	8.675%	$238.3243	$238.32	$238.30	$238.30
Purchase #5	$33.62	11.254%	$37.4036	$37.40	$37.40	$37.40
Purchase #6	$132.46	3.856%	$137.5677	$137.57	$137.55	$137.60
Purchase #7	$112.96	9.444%	$123.6279	$123.63	$123.65	$123.60
7 purchase totals =	$924.01		$1,003.9527	$1,003.95	$1,003.90	$1,003.90