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	$240.69	6.248%	$255.7283	$255.73	$255.75	$255.70
Purchase #2	$136.59	10.258%	$150.6014	$150.60	$150.60	$150.60
Purchase #3	$46.55	5.782%	$49.2415	$49.24	$49.25	$49.20
Purchase #4	$99.79	3.763%	$103.5451	$103.55	$103.55	$103.50
Purchase #5	$160.63	5.415%	$169.3281	$169.33	$169.35	$169.30
Purchase #6	$30.70	5.357%	$32.3446	$32.34	$32.35	$32.30
Purchase #7	$124.25	12.679%	$140.0037	$140.00	$140.00	$140.00
7 purchase totals =	$839.20		$900.7927	$900.79	$900.85	$900.60