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	$91.34	12.495%	$102.7529	$102.75	$102.75	$102.80
Purchase #2	$81.48	4.630%	$85.2525	$85.25	$85.25	$85.30
Purchase #3	$65.33	3.546%	$67.6466	$67.65	$67.65	$67.60
Purchase #4	$145.78	5.637%	$153.9976	$154.00	$154.00	$154.00
Purchase #5	$35.92	9.642%	$39.3834	$39.38	$39.40	$39.40
Purchase #6	$174.80	9.754%	$191.85	$191.85	$191.85	$191.90
Purchase #7	$12.80	8.698%	$13.9133	$13.91	$13.90	$13.90
7 purchase totals =	$607.45		$654.7963	$654.79	$654.80	$654.90