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	$85.79	5.535%	$90.5385	$90.54	$90.55	$90.50
Purchase #2	$50.29	5.874%	$53.244	$53.24	$53.25	$53.20
Purchase #3	$160.28	8.540%	$173.9679	$173.97	$173.95	$174.00
Purchase #4	$176.54	7.431%	$189.6587	$189.66	$189.65	$189.70
Purchase #5	$180.28	3.590%	$186.7521	$186.75	$186.75	$186.80
Purchase #6	$223.89	8.280%	$242.4281	$242.43	$242.45	$242.40
Purchase #7	$213.97	4.327%	$223.2285	$223.23	$223.25	$223.20
7 purchase totals =	$1,091.04		$1,159.8178	$1,159.82	$1,159.85	$1,159.80