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	$132.82	6.853%	$141.9222	$141.92	$141.90	$141.90
Purchase #2	$82.45	9.195%	$90.0313	$90.03	$90.05	$90.00
Purchase #3	$203.89	6.841%	$217.8381	$217.84	$217.85	$217.80
Purchase #4	$71.40	11.121%	$79.3404	$79.34	$79.35	$79.30
Purchase #5	$125.37	8.337%	$135.8221	$135.82	$135.80	$135.80
Purchase #6	$184.97	3.417%	$191.2904	$191.29	$191.30	$191.30
Purchase #7	$89.99	11.822%	$100.6286	$100.63	$100.65	$100.60
7 purchase totals =	$890.89		$956.8731	$956.87	$956.90	$956.70