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	$103.69	13.299%	$117.4797	$117.48	$117.50	$117.50
Purchase #2	$63.81	7.178%	$68.3903	$68.39	$68.40	$68.40
Purchase #3	$190.90	12.650%	$215.0489	$215.05	$215.05	$215.00
Purchase #4	$244.83	11.778%	$273.6661	$273.67	$273.65	$273.70
Purchase #5	$178.37	7.149%	$191.1217	$191.12	$191.10	$191.10
Purchase #6	$31.93	6.405%	$33.9751	$33.98	$34.00	$34.00
Purchase #7	$224.81	3.130%	$231.8466	$231.85	$231.85	$231.80
7 purchase totals =	$1,038.34		$1,131.5284	$1,131.54	$1,131.55	$1,131.50