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	$50.83	8.423%	$55.1114	$55.11	$55.10	$55.10
Purchase #2	$237.80	6.830%	$254.0417	$254.04	$254.05	$254.00
Purchase #3	$97.78	7.537%	$105.1497	$105.15	$105.15	$105.10
Purchase #4	$233.98	9.338%	$255.8291	$255.83	$255.85	$255.80
Purchase #5	$25.33	7.303%	$27.1798	$27.18	$27.20	$27.20
Purchase #6	$123.77	6.584%	$131.919	$131.92	$131.90	$131.90
Purchase #7	$30.25	4.620%	$31.6476	$31.65	$31.65	$31.60
7 purchase totals =	$799.74		$860.8783	$860.88	$860.90	$860.70