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	$139.38	11.557%	$155.4881	$155.49	$155.50	$155.50
Purchase #2	$180.34	9.111%	$196.7708	$196.77	$196.75	$196.80
Purchase #3	$80.51	11.651%	$89.8902	$89.89	$89.90	$89.90
Purchase #4	$127.47	8.810%	$138.7001	$138.70	$138.70	$138.70
Purchase #5	$195.31	6.770%	$208.5325	$208.53	$208.55	$208.50
Purchase #6	$132.28	6.604%	$141.0158	$141.02	$141.00	$141.00
Purchase #7	$250.73	11.690%	$280.0403	$280.04	$280.05	$280.00
7 purchase totals =	$1,106.02		$1,210.4378	$1,210.44	$1,210.45	$1,210.40