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	$149.88	8.689%	$162.9031	$162.90	$162.90	$162.90
Purchase #2	$94.55	10.297%	$104.2858	$104.29	$104.30	$104.30
Purchase #3	$89.62	11.627%	$100.0401	$100.04	$100.05	$100.00
Purchase #4	$125.43	10.176%	$138.1938	$138.19	$138.20	$138.20
Purchase #5	$26.35	10.359%	$29.0796	$29.08	$29.10	$29.10
Purchase #6	$78.38	7.131%	$83.9693	$83.97	$83.95	$84.00
Purchase #7	$172.55	5.480%	$182.0057	$182.01	$182.00	$182.00
7 purchase totals =	$736.76		$800.4774	$800.48	$800.50	$800.50