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	$185.99	6.728%	$198.5034	$198.50	$198.50	$198.50
Purchase #2	$248.31	6.323%	$264.0106	$264.01	$264.00	$264.00
Purchase #3	$128.32	5.136%	$134.9105	$134.91	$134.90	$134.90
Purchase #4	$234.63	9.139%	$256.0728	$256.07	$256.05	$256.10
Purchase #5	$75.77	3.271%	$78.2484	$78.25	$78.25	$78.20
Purchase #6	$180.78	12.331%	$203.072	$203.07	$203.05	$203.10
Purchase #7	$86.78	3.611%	$89.9136	$89.91	$89.90	$89.90
7 purchase totals =	$1,140.58		$1,224.7313	$1,224.72	$1,224.65	$1,224.70