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	$242.78	9.318%	$265.4022	$265.40	$265.40	$265.40
Purchase #2	$50.94	12.825%	$57.4731	$57.47	$57.45	$57.50
Purchase #3	$47.85	11.772%	$53.4829	$53.48	$53.50	$53.50
Purchase #4	$194.35	8.198%	$210.2828	$210.28	$210.30	$210.30
Purchase #5	$172.76	5.198%	$181.7401	$181.74	$181.75	$181.70
Purchase #6	$70.45	4.228%	$73.4286	$73.43	$73.45	$73.40
Purchase #7	$85.57	5.605%	$90.3662	$90.37	$90.35	$90.40
7 purchase totals =	$864.70		$932.1759	$932.17	$932.20	$932.20