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	$54.43	3.378%	$56.2686	$56.27	$56.25	$56.30
Purchase #2	$220.64	7.108%	$236.3231	$236.32	$236.30	$236.30
Purchase #3	$152.60	4.132%	$158.9054	$158.91	$158.90	$158.90
Purchase #4	$62.41	7.361%	$67.004	$67.00	$67.00	$67.00
Purchase #5	$159.76	6.587%	$170.2834	$170.28	$170.30	$170.30
Purchase #6	$117.78	8.855%	$128.2094	$128.21	$128.20	$128.20
Purchase #7	$112.91	9.630%	$123.7832	$123.78	$123.80	$123.80
7 purchase totals =	$880.53		$940.7771	$940.77	$940.75	$940.80