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	$154.63	6.606%	$164.8449	$164.84	$164.85	$164.80
Purchase #2	$158.77	13.332%	$179.9372	$179.94	$179.95	$179.90
Purchase #3	$103.43	7.691%	$111.3848	$111.38	$111.40	$111.40
Purchase #4	$114.86	13.652%	$130.5407	$130.54	$130.55	$130.50
Purchase #5	$247.89	13.619%	$281.6501	$281.65	$281.65	$281.70
Purchase #6	$196.39	4.541%	$205.3081	$205.31	$205.30	$205.30
Purchase #7	$171.35	13.630%	$194.705	$194.71	$194.70	$194.70
7 purchase totals =	$1,147.32		$1,268.3708	$1,268.37	$1,268.40	$1,268.30