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	$38.68	8.601%	$42.0069	$42.01	$42.00	$42.00
Purchase #2	$32.56	4.107%	$33.8972	$33.90	$33.90	$33.90
Purchase #3	$123.86	13.393%	$140.4486	$140.45	$140.45	$140.40
Purchase #4	$205.31	9.256%	$224.3135	$224.31	$224.30	$224.30
Purchase #5	$83.51	10.572%	$92.3387	$92.34	$92.35	$92.30
Purchase #6	$86.33	6.288%	$91.7584	$91.76	$91.75	$91.80
Purchase #7	$154.61	13.869%	$176.0529	$176.05	$176.05	$176.10
7 purchase totals =	$724.86		$800.8162	$800.82	$800.80	$800.80