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	$106.80	9.831%	$117.2995	$117.30	$117.30	$117.30
Purchase #2	$211.61	3.211%	$218.4048	$218.40	$218.40	$218.40
Purchase #3	$61.56	6.270%	$65.4198	$65.42	$65.40	$65.40
Purchase #4	$31.35	4.396%	$32.7281	$32.73	$32.75	$32.70
Purchase #5	$85.81	5.482%	$90.5141	$90.51	$90.50	$90.50
Purchase #6	$7.48	6.232%	$7.9462	$7.95	$7.95	$7.90
Purchase #7	$61.59	8.172%	$66.6231	$66.62	$66.60	$66.60
7 purchase totals =	$566.20		$598.9356	$598.93	$598.90	$598.80