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	$74.78	9.786%	$82.098	$82.10	$82.10	$82.10
Purchase #2	$227.61	12.315%	$255.6402	$255.64	$255.65	$255.60
Purchase #3	$194.41	8.324%	$210.5927	$210.59	$210.60	$210.60
Purchase #4	$38.30	6.430%	$40.7627	$40.76	$40.75	$40.80
Purchase #5	$223.88	6.483%	$238.3941	$238.39	$238.40	$238.40
Purchase #6	$73.32	4.776%	$76.8218	$76.82	$76.80	$76.80
Purchase #7	$247.85	10.382%	$273.5818	$273.58	$273.60	$273.60
7 purchase totals =	$1,080.15		$1,177.8913	$1,177.88	$1,177.90	$1,177.90