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	$83.47	7.289%	$89.5541	$89.55	$89.55	$89.60
Purchase #2	$61.34	11.254%	$68.2432	$68.24	$68.25	$68.20
Purchase #3	$99.74	9.805%	$109.5195	$109.52	$109.50	$109.50
Purchase #4	$100.29	3.146%	$103.4451	$103.45	$103.45	$103.40
Purchase #5	$127.61	9.581%	$139.8363	$139.84	$139.85	$139.80
Purchase #6	$160.43	9.177%	$175.1527	$175.15	$175.15	$175.20
Purchase #7	$228.60	3.763%	$237.2022	$237.20	$237.20	$237.20
7 purchase totals =	$861.48		$922.9531	$922.95	$922.95	$922.90