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	$20.64	11.262%	$22.9645	$22.96	$22.95	$23.00
Purchase #2	$212.95	7.686%	$229.3173	$229.32	$229.30	$229.30
Purchase #3	$72.79	7.217%	$78.0433	$78.04	$78.05	$78.00
Purchase #4	$178.86	3.224%	$184.6264	$184.63	$184.65	$184.60
Purchase #5	$229.46	12.588%	$258.3444	$258.34	$258.35	$258.30
Purchase #6	$86.46	4.734%	$90.553	$90.55	$90.55	$90.60
Purchase #7	$37.94	4.213%	$39.5384	$39.54	$39.55	$39.50
7 purchase totals =	$839.10		$903.3873	$903.38	$903.40	$903.30