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	$139.38	4.229%	$145.2744	$145.27	$145.25	$145.30
Purchase #2	$182.27	6.801%	$194.6662	$194.67	$194.65	$194.70
Purchase #3	$152.92	10.540%	$169.0378	$169.04	$169.05	$169.00
Purchase #4	$223.55	12.253%	$250.9416	$250.94	$250.95	$250.90
Purchase #5	$36.47	13.864%	$41.5262	$41.53	$41.55	$41.50
Purchase #6	$174.78	7.376%	$187.6718	$187.67	$187.65	$187.70
Purchase #7	$75.60	9.511%	$82.7903	$82.79	$82.80	$82.80
7 purchase totals =	$984.97		$1,071.9083	$1,071.91	$1,071.90	$1,071.90