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	$38.47	8.114%	$41.5915	$41.59	$41.60	$41.60
Purchase #2	$238.56	13.772%	$271.4145	$271.41	$271.40	$271.40
Purchase #3	$108.29	4.657%	$113.3331	$113.33	$113.35	$113.30
Purchase #4	$243.90	6.649%	$260.1169	$260.12	$260.10	$260.10
Purchase #5	$81.90	8.522%	$88.8795	$88.88	$88.90	$88.90
Purchase #6	$111.68	5.526%	$117.8514	$117.85	$117.85	$117.90
Purchase #7	$237.85	5.408%	$250.7129	$250.71	$250.70	$250.70
7 purchase totals =	$1,060.65		$1,143.8998	$1,143.89	$1,143.90	$1,143.90