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	$22.37	11.524%	$24.9479	$24.95	$24.95	$24.90
Purchase #2	$89.83	4.697%	$94.0493	$94.05	$94.05	$94.00
Purchase #3	$138.83	5.679%	$146.7142	$146.71	$146.70	$146.70
Purchase #4	$42.77	6.216%	$45.4286	$45.43	$45.45	$45.40
Purchase #5	$167.40	7.620%	$180.1559	$180.16	$180.15	$180.20
Purchase #6	$97.79	5.232%	$102.9064	$102.91	$102.90	$102.90
Purchase #7	$233.89	12.313%	$262.6889	$262.69	$262.70	$262.70
7 purchase totals =	$792.88		$856.8912	$856.90	$856.90	$856.80