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	$35.86	10.794%	$39.7307	$39.73	$39.75	$39.70
Purchase #2	$88.35	6.359%	$93.9682	$93.97	$93.95	$94.00
Purchase #3	$83.41	6.817%	$89.0961	$89.10	$89.10	$89.10
Purchase #4	$126.83	9.687%	$139.116	$139.12	$139.10	$139.10
Purchase #5	$92.96	7.807%	$100.2174	$100.22	$100.20	$100.20
Purchase #6	$178.25	4.334%	$185.9754	$185.98	$186.00	$186.00
Purchase #7	$136.42	7.144%	$146.1658	$146.17	$146.15	$146.20
7 purchase totals =	$742.08		$794.2696	$794.29	$794.25	$794.30