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	$44.51	7.334%	$47.7744	$47.77	$47.75	$47.80
Purchase #2	$84.54	4.668%	$88.4863	$88.49	$88.50	$88.50
Purchase #3	$55.64	12.497%	$62.5933	$62.59	$62.60	$62.60
Purchase #4	$42.72	6.823%	$45.6348	$45.63	$45.65	$45.60
Purchase #5	$18.67	7.812%	$20.1285	$20.13	$20.15	$20.10
Purchase #6	$212.86	4.273%	$221.9555	$221.96	$221.95	$222.00
Purchase #7	$229.47	5.608%	$242.3387	$242.34	$242.35	$242.30
7 purchase totals =	$688.41		$728.9115	$728.91	$728.95	$728.90