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	$86.64	5.593%	$91.4858	$91.49	$91.50	$91.50
Purchase #2	$156.58	3.266%	$161.6939	$161.69	$161.70	$161.70
Purchase #3	$32.71	13.637%	$37.1707	$37.17	$37.15	$37.20
Purchase #4	$95.79	4.661%	$100.2548	$100.25	$100.25	$100.30
Purchase #5	$128.90	10.587%	$142.5466	$142.55	$142.55	$142.50
Purchase #6	$215.89	12.349%	$242.5503	$242.55	$242.55	$242.60
Purchase #7	$153.83	4.664%	$161.0046	$161.00	$161.00	$161.00
7 purchase totals =	$870.34		$936.7067	$936.70	$936.70	$936.80