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	$35.25	8.228%	$38.1504	$38.15	$38.15	$38.20
Purchase #2	$217.39	7.159%	$232.953	$232.95	$232.95	$233.00
Purchase #3	$41.39	3.620%	$42.8883	$42.89	$42.90	$42.90
Purchase #4	$38.98	8.403%	$42.2555	$42.26	$42.25	$42.30
Purchase #5	$142.78	9.108%	$155.7844	$155.78	$155.80	$155.80
Purchase #6	$67.26	3.414%	$69.5563	$69.56	$69.55	$69.60
Purchase #7	$59.64	10.525%	$65.9171	$65.92	$65.90	$65.90
7 purchase totals =	$602.69		$647.5050	$647.51	$647.50	$647.70