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	$80.52	7.689%	$86.7112	$86.71	$86.70	$86.70
Purchase #2	$191.82	13.766%	$218.2259	$218.23	$218.25	$218.20
Purchase #3	$214.94	6.691%	$229.3216	$229.32	$229.30	$229.30
Purchase #4	$113.54	10.420%	$125.3709	$125.37	$125.35	$125.40
Purchase #5	$179.91	10.361%	$198.5505	$198.55	$198.55	$198.60
Purchase #6	$115.88	9.628%	$127.0369	$127.04	$127.05	$127.00
Purchase #7	$25.33	11.522%	$28.2485	$28.25	$28.25	$28.20
7 purchase totals =	$921.94		$1,013.4655	$1,013.47	$1,013.45	$1,013.40