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	$137.42	6.170%	$145.8988	$145.90	$145.90	$145.90
Purchase #2	$212.72	11.804%	$237.8295	$237.83	$237.85	$237.80
Purchase #3	$98.34	11.770%	$109.9146	$109.91	$109.90	$109.90
Purchase #4	$157.57	13.256%	$178.4575	$178.46	$178.45	$178.50
Purchase #5	$173.85	7.815%	$187.4364	$187.44	$187.45	$187.40
Purchase #6	$157.28	4.830%	$164.8766	$164.88	$164.90	$164.90
Purchase #7	$207.89	13.486%	$235.926	$235.93	$235.95	$235.90
7 purchase totals =	$1,145.07		$1,260.3394	$1,260.35	$1,260.40	$1,260.30