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	$64.40	11.464%	$71.7828	$71.78	$71.80	$71.80
Purchase #2	$100.47	9.354%	$109.868	$109.87	$109.85	$109.90
Purchase #3	$55.86	6.388%	$59.4283	$59.43	$59.45	$59.40
Purchase #4	$27.52	13.801%	$31.318	$31.32	$31.30	$31.30
Purchase #5	$220.39	10.685%	$243.9387	$243.94	$243.95	$243.90
Purchase #6	$140.94	12.196%	$158.129	$158.13	$158.15	$158.10
Purchase #7	$243.88	4.373%	$254.5449	$254.54	$254.55	$254.50
7 purchase totals =	$853.46		$929.0097	$929.01	$929.05	$928.90