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	$34.95	7.556%	$37.5908	$37.59	$37.60	$37.60
Purchase #2	$190.64	3.207%	$196.7538	$196.75	$196.75	$196.80
Purchase #3	$230.30	8.702%	$250.3407	$250.34	$250.35	$250.30
Purchase #4	$42.25	5.423%	$44.5412	$44.54	$44.55	$44.50
Purchase #5	$221.80	3.633%	$229.858	$229.86	$229.85	$229.90
Purchase #6	$80.35	3.490%	$83.1542	$83.15	$83.15	$83.20
Purchase #7	$155.82	3.378%	$161.0836	$161.08	$161.10	$161.10
7 purchase totals =	$956.11		$1,003.3223	$1,003.31	$1,003.35	$1,003.40