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	$249.54	6.329%	$265.3334	$265.33	$265.35	$265.30
Purchase #2	$50.76	13.241%	$57.4811	$57.48	$57.50	$57.50
Purchase #3	$129.60	10.455%	$143.1497	$143.15	$143.15	$143.10
Purchase #4	$154.59	9.254%	$168.8958	$168.90	$168.90	$168.90
Purchase #5	$156.98	6.141%	$166.6201	$166.62	$166.60	$166.60
Purchase #6	$242.44	6.616%	$258.4798	$258.48	$258.50	$258.50
Purchase #7	$136.85	11.233%	$152.2224	$152.22	$152.20	$152.20
7 purchase totals =	$1,120.76		$1,212.1823	$1,212.18	$1,212.20	$1,212.10