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	$139.51	12.461%	$156.8943	$156.89	$156.90	$156.90
Purchase #2	$228.99	9.825%	$251.4883	$251.49	$251.50	$251.50
Purchase #3	$97.80	5.767%	$103.4401	$103.44	$103.45	$103.40
Purchase #4	$40.37	12.616%	$45.4631	$45.46	$45.45	$45.50
Purchase #5	$30.41	4.342%	$31.7304	$31.73	$31.75	$31.70
Purchase #6	$110.92	7.301%	$119.0183	$119.02	$119.00	$119.00
Purchase #7	$78.52	13.242%	$88.9176	$88.92	$88.90	$88.90
7 purchase totals =	$726.52		$796.9521	$796.95	$796.95	$796.90