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	$14.61	5.368%	$15.3943	$15.39	$15.40	$15.40
Purchase #2	$11.76	9.713%	$12.9022	$12.90	$12.90	$12.90
Purchase #3	$126.69	8.407%	$137.3408	$137.34	$137.35	$137.30
Purchase #4	$28.71	3.802%	$29.8016	$29.80	$29.80	$29.80
Purchase #5	$42.34	7.692%	$45.5968	$45.60	$45.60	$45.60
Purchase #6	$171.46	5.219%	$180.4085	$180.41	$180.40	$180.40
Purchase #7	$100.64	4.705%	$105.3751	$105.38	$105.40	$105.40
7 purchase totals =	$496.21		$526.8193	$526.82	$526.85	$526.80