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	$62.67	8.463%	$67.9738	$67.97	$67.95	$68.00
Purchase #2	$137.62	10.872%	$152.582	$152.58	$152.60	$152.60
Purchase #3	$183.27	3.120%	$188.988	$188.99	$189.00	$189.00
Purchase #4	$90.48	10.789%	$100.2419	$100.24	$100.25	$100.20
Purchase #5	$171.55	13.404%	$194.5446	$194.54	$194.55	$194.50
Purchase #6	$95.42	9.726%	$104.7005	$104.70	$104.70	$104.70
Purchase #7	$73.54	11.345%	$81.8831	$81.88	$81.90	$81.90
7 purchase totals =	$814.55		$890.9139	$890.90	$890.95	$890.90