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	$88.25	13.693%	$100.3341	$100.33	$100.35	$100.30
Purchase #2	$134.44	6.705%	$143.4542	$143.45	$143.45	$143.50
Purchase #3	$192.58	11.609%	$214.9366	$214.94	$214.95	$214.90
Purchase #4	$58.78	4.673%	$61.5268	$61.53	$61.55	$61.50
Purchase #5	$137.91	13.690%	$156.7899	$156.79	$156.80	$156.80
Purchase #6	$203.36	13.791%	$231.4054	$231.41	$231.40	$231.40
Purchase #7	$176.51	3.658%	$182.9667	$182.97	$182.95	$183.00
7 purchase totals =	$991.83		$1,091.4137	$1,091.42	$1,091.45	$1,091.40