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	$21.77	4.610%	$22.7736	$22.77	$22.75	$22.80
Purchase #2	$128.48	8.125%	$138.919	$138.92	$138.90	$138.90
Purchase #3	$250.89	7.408%	$269.4759	$269.48	$269.50	$269.50
Purchase #4	$48.38	9.231%	$52.846	$52.85	$52.85	$52.80
Purchase #5	$209.88	6.212%	$222.9177	$222.92	$222.90	$222.90
Purchase #6	$91.76	8.357%	$99.4284	$99.43	$99.45	$99.40
Purchase #7	$104.99	12.419%	$118.0287	$118.03	$118.05	$118.00
7 purchase totals =	$856.15		$924.3893	$924.40	$924.40	$924.30