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	$150.48	3.362%	$155.5391	$155.54	$155.55	$155.50
Purchase #2	$171.47	13.428%	$194.495	$194.50	$194.50	$194.50
Purchase #3	$250.91	4.589%	$262.4243	$262.42	$262.40	$262.40
Purchase #4	$155.89	5.605%	$164.6276	$164.63	$164.65	$164.60
Purchase #5	$27.82	13.252%	$31.5067	$31.51	$31.50	$31.50
Purchase #6	$120.88	10.191%	$133.1989	$133.20	$133.20	$133.20
Purchase #7	$33.25	6.445%	$35.393	$35.39	$35.40	$35.40
7 purchase totals =	$910.70		$977.1846	$977.19	$977.20	$977.10