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	$137.38	9.772%	$150.8048	$150.80	$150.80	$150.80
Purchase #2	$82.26	9.754%	$90.2836	$90.28	$90.30	$90.30
Purchase #3	$30.74	10.568%	$33.9886	$33.99	$34.00	$34.00
Purchase #4	$149.70	12.311%	$168.1296	$168.13	$168.15	$168.10
Purchase #5	$195.25	9.419%	$213.6406	$213.64	$213.65	$213.60
Purchase #6	$168.98	6.813%	$180.4926	$180.49	$180.50	$180.50
Purchase #7	$82.97	10.399%	$91.5981	$91.60	$91.60	$91.60
7 purchase totals =	$847.28		$928.9379	$928.93	$929.00	$928.90