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	$47.86	7.696%	$51.5433	$51.54	$51.55	$51.50
Purchase #2	$142.51	10.300%	$157.1885	$157.19	$157.20	$157.20
Purchase #3	$65.69	9.627%	$72.014	$72.01	$72.00	$72.00
Purchase #4	$117.79	8.392%	$127.6749	$127.67	$127.65	$127.70
Purchase #5	$7.25	5.261%	$7.6314	$7.63	$7.65	$7.60
Purchase #6	$126.50	11.768%	$141.3865	$141.39	$141.40	$141.40
Purchase #7	$248.98	9.764%	$273.2904	$273.29	$273.30	$273.30
7 purchase totals =	$756.58		$830.7290	$830.72	$830.75	$830.70