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	$138.59	9.843%	$152.2314	$152.23	$152.25	$152.20
Purchase #2	$72.54	8.332%	$78.584	$78.58	$78.60	$78.60
Purchase #3	$80.51	3.865%	$83.6217	$83.62	$83.60	$83.60
Purchase #4	$162.43	13.458%	$184.2898	$184.29	$184.30	$184.30
Purchase #5	$151.62	13.359%	$171.8749	$171.87	$171.85	$171.90
Purchase #6	$21.29	6.243%	$22.6191	$22.62	$22.60	$22.60
Purchase #7	$93.97	6.740%	$100.3036	$100.30	$100.30	$100.30
7 purchase totals =	$720.95		$793.5245	$793.51	$793.50	$793.50